How to Make It
Preheat oven to 425°F. Toss together potatoes, shallots, 1 tablespoon of the oil, and 1⁄4 teaspoon of the salt on a large rimmed baking sheet. Arrange mixture in an even layer, with potatoes facing cut sides down. Roast until almost tender, about 15 minutes. Remove from oven.
While potato mixture roasts, stir together 3 tablespoons of the mustard, 1⁄4 teaspoon of the salt, and 1 teaspoon of the honey in a small bowl. Stir together panko, thyme, 1 tablespoon of the oil, and 1⁄4 teaspoon of the salt in a separate small bowl. Arrange salmon fillets, skin side down, on a plate. Spread mustard mixture evenly over skinless tops of fillets. Sprinkle tops evenly with panko mixture, pressing to adhere.
Stir roasted potato mixture on baking sheet, pushing mixture toward edges of baking sheet with a spatula. Place salmon filets, skin side down, in center of baking sheet. Scatter sugar snap peas evenly around salmon. Return baking sheet to oven. Bake at 425°F until panko crust is golden brown, salmon is cooked to medium doneness (turns flaky and opaque), and potatoes are tender, about 10 minutes.
Meanwhile, whisk together vinegar, garlic, smoked paprika, and remaining 2 tablespoons oil, 1⁄4 teaspoon salt, 2 teaspoons mustard, and 1⁄2 teaspoon honey in a small bowl until combined.
Divide salmon fillets and vegetable mixture evenly among 4 plates. Drizzle vegetable mixture evenly with vinaigrette.