Preheat the oven to 350°F and generously grease a 9x13-inch baking dish with cooking spray.
Bring a large pot of water to a boil and add 2 teaspoons salt when boiling.
Trim snap peas, peel and slice the carrot into coins, halve the cherry tomatoes, and thinly slice the mushrooms, mini peppers, and summer squash.
Cook tortellini according to package directions; in the last 2 minutes of cooking, add the snap peas and carrot. Drain and transfer the tortellini and vegetables to the prepared casserole dish.
While the pasta cooks, heat olive oil in a skillet over medium-high heat and sauté mushrooms, peppers, and summer squash until crisp-tender, about 5 minutes.
Add the sautéed vegetables, halved cherry tomatoes, and frozen corn to the casserole dish with the tortellini and gently toss to combine.
In a small saucepan over medium heat, melt the butter, whisk in the flour and cook 1 minute to make a paste, then slowly whisk in the vegetable stock until smooth.
Gradually whisk in the milk and continue stirring until the sauce thickens, then stir in roasted garlic powder, salt, pepper, dried basil, and Italian seasoning.
Soften the cream cheese in the microwave if needed, then whisk it into the hot sauce until completely smooth; taste and adjust seasonings.
Pour the cream sauce over the tortellini and vegetables, stir gently to coat evenly, and smooth into an even layer in the dish. Sprinkle the grated Parmesan over the top.
Bake for 20–25 minutes until heated through and the cheese is melted; broil 1–2 minutes at the end if you want a browned top. Serve hot with optional pesto.