Preheat and prep: Heat the oven to 425°F (220°C).
Line a large baking sheet with parchment for easy cleanup. Bring a large pot of salted water to a boil.
Toss the veggies: On the baking sheet, combine tomatoes, zucchini, red bell pepper, red onion, and broccoli. Drizzle with 2 tablespoons olive oil.
Season with salt, pepper, and garlic powder. Toss to coat and spread in a single layer.
Roast until caramelized: Roast for 18–22 minutes, stirring once halfway through, until the edges are golden and the tomatoes are juicy.
Cook the tortellini: While the veggies roast, add tortellini to the boiling water. Cook according to package directions, usually 2–4 minutes, until they float and are tender.
Reserve 1/2 cup of pasta water, then drain.
Loosen the pesto: In a large bowl or the empty pasta pot, stir the pesto with 1 tablespoon olive oil and a splash of the reserved pasta water to create a silky sauce.
Combine: Add the hot tortellini to the pesto and toss gently to coat. Fold in the roasted vegetables, lemon zest, and half the lemon juice. If needed, add more pasta water a tablespoon at a time until glossy.
Finish and taste: Stir in Parmesan.
Taste and adjust with more salt, pepper, or lemon juice. Add red pepper flakes if you like a little heat.
Serve: Divide into bowls and top with extra Parmesan and torn basil. Serve warm.