Start by preheating your oven to 400°F (200°C). Line a large rimmed baking sheet with parchment paper or foil for easy cleanup. Lightly drizzle the surface with olive oil to prevent sticking and enhance flavor.
Place the salmon fillets on the sheet pan, skin-side down if applicable. Drizzle each fillet with olive oil, then season with salt, pepper, garlic powder, and paprika. Top each with a lemon slice and a pinch of lemon zest for brightness.
In a mixing bowl, toss the bell peppers, zucchini, red onion, and cherry tomatoes with a tablespoon of olive oil, salt, and pepper. Arrange the vegetables around the salmon on the sheet pan, leaving space for even roasting.
Roast in the preheated oven for 18–20 minutes, or until the salmon flakes easily with a fork and the vegetables are tender with crispy edges. If you like the veggies extra roasted, you can remove the salmon after 16–18 minutes and continue roasting the veggies for an additional 5 minutes.
Once cooked, remove the pan from the oven and let it rest for a few minutes. Sprinkle chopped parsley and, if desired, red pepper flakes over the top for extra flavor and color.
Use a spatula to gently lift the salmon and transfer to plates alongside the roasted vegetables. Serve with lemon wedges or a drizzle of your favorite sauce like tzatziki or a garlic yogurt dressing.