Preheat oven to 400°F and line a large sheet pan with parchment paper or aluminum foil.
Arrange the halved potatoes and broccoli florets on the sheet pan, drizzle with 2 tablespoons olive oil, and season with half of the garlic powder, Italian seasoning, salt, and pepper.
Push the vegetables to the sides of the pan and place salmon fillets in the center, then drizzle with remaining 1 tablespoon olive oil and season with remaining spices.
Top each salmon fillet with a lemon slice and arrange remaining lemon slices around the vegetables.
Bake for 18-22 minutes until salmon flakes easily with a fork and vegetables are tender and lightly browned.