Preheat the oven to 375°F. Line a rimmed baking sheet with foil.
Spread the sauce evenly on the baking sheet. Top with the peppers and onion wedges. Drizzle with the oil and season with salt and pepper. Toss to coat. Bake for 15 minutes. Nestle the meatballs on top and return to the oven for 15 minutes. Sprinkle the cheese evenly over the top and bake for another 5 minutes or until the cheese has melted.