Preheat the oven to 400°F (200°C).
Line a large sheet pan with parchment paper or lightly grease it with 1 tablespoon of olive oil.
In a large bowl, combine the halved baby potatoes, red bell pepper pieces, yellow bell pepper pieces, zucchini slices, and cherry tomatoes.
Drizzle 2 tablespoons of olive oil over the vegetables. Sprinkle with garlic powder, dried oregano, paprika, salt, and black pepper. Toss well to coat evenly.
Spread the seasoned vegetables in a single layer on the prepared sheet pan.
Place the sheet pan in the oven and roast the vegetables for 10 minutes.
Remove the sheet pan from the oven. Push the vegetables to the sides to make space in the center for the salmon fillets.
Place the salmon fillets skin-side down in the center of the sheet pan.
Season the salmon fillets with salt and black pepper. Lay lemon slices on top of each fillet.
Return the sheet pan to the oven and roast for an additional 10 minutes, or until the salmon is cooked through and flakes easily with a fork, and the vegetables are tender.
Remove from the oven and sprinkle chopped fresh parsley over the salmon and vegetables.
Serve immediately, spooning the roasted vegetables alongside the salmon.