Cook the Tortellini:
Fill a large pot with water and add 1 tablespoon olive oil. Bring to a rolling boil, then stir in the tortellini. Cook for about 7 minutes or until the tortellini float to the top and the filling is hot. Drain and transfer to a large bowl.
Sauté the Mushrooms and Vegetables:
In a large saucepan, melt 2 tablespoons of butter over medium-high heat. Add the mushrooms, onion, and garlic, and sauté until the vegetables are softened, about 5 minutes. Use a slotted spoon to remove the mushroom mixture from the pan and add it to the bowl with the tortellini.
Make the Alfredo Sauce:
Drain any excess liquid from the mushrooms in the saucepan. Reduce heat to medium and melt the remaining 6 tablespoons of butter in the pan. Stir in the half-and-half, salt, black pepper, garlic powder, and a pinch of cayenne pepper. Cook, stirring occasionally, until the sauce is thick and bubbly, about 10 minutes. Gradually stir in the Parmesan cheese until melted and the sauce has thickened.
Combine and Serve:
Pour the Alfredo sauce over the tortellini and mushroom mixture, tossing to combine everything. Serve in bowls, and garnish with fresh thyme for added flavor. Enjoy!