Directions

1. Place racks in upper and lower thirds of oven; preheat to 425°F. Cut 1 baguette in half lengthwise, then crosswise. Mix ½ cup (1 stick) unsalted butter, room temperature, 3 garlic cloves, finely grated, and 1 Tbsp. extra-virgin olive oil in a small bowl. Spread over cut sides of bread. Top with ⅓ cup finely grated Parmesan; season with kosher salt and freshly ground pepper. Place bread, cut side up, on a rimmed baking sheet; set aside.
2. Cut half of 3 pints cherry tomatoes (about 5 cups) in half. Place all of the tomatoes in a medium bowl; add 1½ cups sliced roasted red peppers from a jar. Drizzle with oil, season with salt and black pepper, and toss to coat.
3. Place 1 red onion, coarsely chopped, on a second rimmed baking sheet; drizzle with oil. Season with salt and black pepper; toss to coat. Arrange in a single layer; roast on top rack until starting to brown, about 5 minutes. Add tomato mixture and roast until tomatoes soften, 10–12 minutes.
4. Place meatballs throughout vegetables; drizzle with oil. Roast, shaking pan once, until meatballs are cooked through and most of the tomatoes have burst, 15-20 minutes.
5. Meanwhile, bake reserved garlic bread on bottom rack until golden brown, 8–10 minutes.
6. Divide meatball mixture among plates and top with basil leaves and Parmesan. Serve with garlic bread.