Bring a large pot of lightly salted water to a boil.
While the water heats, finish prep: chop 1 medium yellow onion (about 1 1/2 cups), cut kernels from 2 ears corn (about 2 cups), measure 2 cups (12 oz) grape tomatoes, slice 2 medium zucchini (12 oz total) into 1/4-inch-thick half-moons, mince 3 garlic cloves (about 1 Tbsp), and chop 1/4 cup basil and 1/4 cup parsley.
In a 12-inch sauté pan or deep skillet, heat 2 Tbsp extra-virgin olive oil over medium-high heat.
Add the chopped onion and sauté until softened, about 3 minutes.
Add the corn kernels and sauté 2 minutes more.
Add the grape tomatoes and sauté 3 minutes.
Add the sliced zucchini and minced garlic and continue to sauté until the zucchini is tender and many of the tomatoes have burst, about 6 to 8 minutes. As you begin this 6–8 minute stage, add the 20 oz refrigerated tortellini to the boiling water and cook the tortellini according to package directions but stop 1 minute before the package’s stated time.
When the tortellini is nearly done, reserve about 1/4 cup of the pasta cooking water, then drain the tortellini.
Add the drained tortellini and 1 1/4 cups marinara sauce to the pan with the vegetables. Cook and toss until the tortellini finishes cooking and everything is heated through, about 1 to 2 minutes; if the sauce seems too thick, add a splash of the reserved pasta water to loosen it.
Remove the pan from the heat. Season with salt and freshly ground black pepper to taste, then toss in 1/4 cup of the finely shredded Parmesan, the chopped basil, and the chopped parsley.
Serve immediately, topping individual servings with the remaining 1/4 cup finely shredded Parmesan.