Preheat oven to 425°F (220°C). Toss potato wedges with 1 tbsp oil, 1/2 tsp salt, and smoked paprika on a rimmed sheet pan; roast 10 minutes.
Add halved Brussels sprouts tossed with remaining oil, 1/4 tsp salt, and pepper; push veggies aside to make room.
Pat salmon dry, brush with Dijon mixed with honey if using, sprinkle with remaining salt and pepper, and place skin-side down on the sheet pan.
Add lemon slices around the fish and return pan to oven; roast 10–12 minutes until salmon flakes and veggies are browned.
Let rest 2 minutes, squeeze extra lemon, and serve immediately.