How to Make It
Scrub 1 (8-oz.) russet potato; pierce potato all over with a fork. Place in a medium-size microwavable bowl, and rub potato with 1/4 tsp. olive oil. Microwave on HIGH until mostly tender, about 5 minutes. Flip potato, and microwave on HIGH until fully tender, about 2 to 3 more minutes. Let stand 5 minutes.
Preheat broiler with oven rack 6 inches from heat. Thinly slice 2 small garlic cloves, and chop 2 cups firmly packed baby spinach. Cook garlic in 1/2 tsp. olive oil in a skillet over medium, stirring often, until softened and lightly golden, about 2 to 3 minutes. Add spinach, and cook, stirring occasionally, until wilted, about 1 minute. Remove spinach mixture from heat, and set aside.
Cut potato in half, and scoop out pulp into a bowl, leaving 1/4-inch-thick shells. Mash pulp with 1 1/2 Tbsp. warm whole milk, 2 1/2 tsp. olive oil, 1/4 tsp. kosher salt, and 1/8 tsp. black pepper until mostly smooth. Fold in spinach mixture. Spoon into shells, and place on a baking sheet. Top evenly with 2 Tbsp. feta cheese. Broil until lightly browned and warmed through, 2 to 3 minutes. Sprinkle evenly with 1 tsp. chopped fresh dill and 1/4 tsp. lemon zest.