Marinated Cucumber, Tomato, and Onion Salad

The twist on this classic Southern summer salad is a rest in an overnight marinade. The flavors of the dressing pull the natural juices out of the vegetables, which then get re-absorbed into them for a punchy, juicy salad that is at once refreshing and comforting.

The cucumbers and onions take on an almost pickled texture, while the tomatoes get slightly slumpy—a great way to either celebrate the ripest of heirloom garden tomatoes, or to salvage some less-than-perfect grocery store varieties. And since you make it a day ahead, it's the ideal pre-prepped dish for your next backyard gathering or potluck offering.

But one of my favorite things about it is that it is endlessly adaptable for whatever style of salad tickles your fancy. This versatile salad can be eaten as-is, piled on top of lettuce or greens, or forked through cooked pasta or rice. Add crushed crunchy pita chips for a riff on Fattoush or toasted torn pieces of sourdough for a version of a panzanella.

The secret pro-tip? Any leftovers can be whizzed up in your blender for an instant gazpacho! Give this simple salad a shot, and get ready to be inspired. This recipe serves 4 to 6 people, but can be doubled for a crowd.

What's in a Cucumber Tomato Onion Salad?

When you're making a simple salad like this cucumber tomato onion salad, it's imperative the ingredients you use are as fresh and bright as possible. Why? When so few ingredients are used, you taste every single one of them. So while this salad is quite humble in its ingredient list, focus on quality, and the results will be stellar.

Heirloom Tomatoes
This recipe for cucumber, tomato, and onion salad calls for heirloom tomatoes, preferably beefsteaks. The meatier the tomato, the better it will absorb and stand up to the marinade in the overnight soak. (These tomatoes also make the ideal Southern Tomato Sandwich.) But heirloom beefsteaks are pricier, so if you're looking to not drop a few bucks on each tomato, just go for the highest quality tomato you can afford. The tomatoes share the spotlight in this salad, so their quality is important.

If you're craving this salad out of tomato season, reach for Romas or cherry tomatoes instead. Just slice or chop them up a bit more so the flavors of the marinade can really soak in.

English Cucumbers
English cucumbers are the preference for this cucumber tomato onion salad because they often have thinner skins and are slightly sweeter than Kirbys. Though this recipe calls for peeling the cucumbers, you don't have to—in which case, the English cucumbers really will be preferred.

Red Onions
You might think we'd call for Vidalia onions in this cucumber salad, but we're steering toward the reds here because they are spicier and can stand up to the long soak in the marinade. Sweeter onions, like Vidalia or yellow onions, have enough bite that they could be used, but because they're already a bit mellow, you may lose some zip after they've marinated.

Vinegar
This recipe for cucumber tomato onion salad calls for sherry vinegar or red wine vinegar, both of which have a slightly sweet edge to the vinegar bite. But you can actually use any vinegar you like or have. Even plain white distilled vinegar would work, but you may want to amp up the sweetness a bit by adding a pinch of sugar to the marinade.

Herbs
There are herbs in the marinade and herbs as a garnish. We like herbs de Provence, a blend of thyme, tarragon, basil, rosemary, oregano, and a few others, because it's a rich and warming mix. But it can be expensive and difficult to find, so a traditional Italian herb mix can work, too. That's basil, oregano, thyme, marjoram, and rosemary. If you don't have either, DIY your own mix with equal parts of these dried herbs.

For the finishing herb garnish, you can stick with something already in the salad—a sprinkle of fresh basil would certainly sing the sounds of summer—or mix it up with something a bit brighter and grassier, like chives or chervil.

How to Make Cucumber Tomato Onion Salad

The process of making cucumber tomato onion salad is incredibly simple. With all the chopping and mixing, everything is done in about 10 minutes, 15 if you double the recipe for a big crowd. But you have to wait 12 to 24 hours before this salad is ready to eat. And that's the hard part.

Step 1. Make the dressing

In a small bowl, combine the olive oil, vinegar, dried herbs, salt, and black pepper. Crushed red pepper flakes are optional. They infuse a hint of heat in this, which is elevated by the vinegar-based dressing.

Not sure which you'd like better? Split the dressing and the vegetables to make one with the pepper and one without. Sensitive palates and kid eaters will appreciate the option.

Step 2. Add the vegetables

Pour the dressing over the bowl of prepared cucumbers, tomatoes, and onions. Gently toss to coat.

Leave the bowl sitting on the counter for 1 hour. This gives the marinade time to soften the vegetables and begin to pull out some of their natural juices. After an hour, give the cucumber, tomato, and onion salad a quick stir, then cover the bowl with plastic wrap or a lid and slide into your fridge.

Step 3. Marinate

Let the salad sit overnight in the fridge, or up to 24 hours. Every few hours, stir the salad a bit to recoat the vegetables with the dressing. This will help infuse the tomatoes, cucumbers, and onions with the flavorful dressing.

Step 4. Bring to room temp before serving

Before you serve this salad, bring it out of the fridge, and let it sit at room temperature for 30 minutes to an hour. In this time, the vegetables will warm slightly, helping release the natural juices that are now beautifully mingled with the dressing. Give the salad a few turns with a spoon, and top with any fresh herbs of your choosing.

How to Store Cucumber Tomato Onion Salad

Obviously this salad can be stored in the fridge. After the initial 12 to 24 hours marinade, you can keep it in the cooler for up to another 4 days. However, keep in mind that the vegetables will continue to soften as they sit, so by the end, they may be quite tender.

No worries, though! Give the vegetables and a spoonful or two of the marinade a quick buzz in a food processor, and you've got a fresh summer salsa. Keep going, with a bit more leftover juice, and you've got gazpacho. Or finish up the vegetables, and take the marinade for use as a fresh and effortless salad dressing. This is the summer gift that keeps on going.

More Cucumber Salads

- Creamy Cucumber Salad
- Spicy Cucumber Onion Salad
- Sesame, Tomato, and Cucumber Salad

Editorial contributions by Kimberly Holland.