Preheat oven to 425°F (220°C). Toss potatoes and Brussels sprouts with 1 tbsp oil, salt, pepper, and smoked paprika; spread on a large rimmed baking sheet. Roast 15 minutes.
Whisk maple syrup, Dijon, soy sauce, garlic, and remaining 1 tbsp oil in a bowl. Pat salmon dry and season lightly with salt and pepper.
Push veggies to the sides of the sheet; place salmon skin-side down in the center. Brush half the glaze over salmon and a bit on veggies.
Roast 10–12 more minutes until potatoes are tender and salmon flakes with a fork. Brush remaining glaze, broil 1–2 minutes if you want more color.
Squeeze lemon over everything and garnish with parsley before serving.