Heat a nonstick skillet over medium-high heat. Cook and stir sausage in the hot skillet until browned, about 10 minutes.

Heat olive oil in a large pot over medium-high heat. Add onion and garlic; saute until the onion is translucent, about 5 minutes. Reduce heat; add tomatoes, spinach, mushrooms, basil, salt, and pepper. Bring to a simmer, stirring as needed.

Combine cream, milk, cheese, and flour in a bowl. Add to the tomato mixture and return to a simmer. Stir occasionally until reduced, about 15 minutes.

While the sauce is reducing, bring a large pot of water to a boil. Add tortellini and boil gently until tender, about 6 minutes. Drain the tortellini. Mix with the tomato sauce and serve.