Preheat the oven to 400°F and line a large sheet pan with parchment paper.

Pat the salmon fillets very dry with paper towels and place them on a plate.

In a small bowl, stir together 1/2 tsp salt, 1/4 tsp black pepper, garlic powder, paprika, and brown sugar.

Sprinkle the spice mixture evenly over both sides of the salmon fillets and gently rub it in.

Add the broccoli florets, bell pepper slices, and red onion slices to the prepared sheet pan.

Drizzle the vegetables with 2 tbsp olive oil, then sprinkle with the remaining 1/2 tsp salt and 1/4 tsp black pepper and toss to coat.

Spread the vegetables in a single layer on the pan, leaving spaces to nestle the salmon.

Nestle the seasoned salmon fillets on top of the vegetables, skin side down if using skin-on fillets.

Brush the tops of the salmon with the remaining 1 tbsp olive oil.

Bake for 12 to 15 minutes, until the salmon flakes easily with a fork but is still slightly glossy in the center and the vegetables are tender.

If you want a more golden top, switch the oven to broil and broil the salmon and vegetables for 1 to 2 minutes, watching closely.

While the salmon bakes, whisk together the lemon juice, lemon zest, Dijon mustard, honey, and chopped parsley in a small bowl.

Remove the sheet pan from the oven and immediately spoon the lemon Dijon sauce over the salmon and vegetables.

Let everything rest on the pan for 3 minutes, then serve directly from the pan or transfer to plates.