Preheat the oven to 425°F (220°C). Line a rimmed 18 x 13-inch baking sheet or use it unlined.
Place the sliced zucchini, yellow squash, diced red bell pepper, diced red onion, and sliced mushrooms on the baking sheet.
Drizzle the vegetables with 2 tablespoons olive oil, season with salt and freshly ground black pepper, and toss on the sheet to coat evenly.
Roast the vegetables 10 minutes, then remove the sheet, add the halved tomatoes and minced garlic, and toss to combine.
Return the sheet to the oven and roast 10 more minutes, or until the vegetables are tender. Remove the sheet, add the fresh spinach, and toss; roast 1 minute longer until the spinach wilts.
While the vegetables roast, cook the refrigerated three-cheese tortellini in a large pot of boiling salted water according to package directions; drain well in a colander.
Transfer the drained tortellini to a large bowl. Add the roasted vegetables and 2/3 cup pesto, then season with salt and pepper to taste and toss gently to coat everything evenly.
Serve warm and top each portion with finely shredded Parmesan cheese as desired.
