Pre-heat oven to 350F.
Spray a 9 x 13-inch glass baking dish with non-stick cooking spray and set aside.
In a large skillet, sauté sausage with onion, mushrooms, and red bell pepper in the olive oil, breaking up the sausage with a fork, until the meat is browned and the vegetables are tender; drain, if necessary.
Sprinkle flour over the meat mixture and cook for 1 to 2 minutes.
Add the pasta sauce and water to the skillet and bring to a simmer.
Remove the skillet from the heat and stir in the frozen tortellini and the pesto sauce; spread in prepared pan.
Top with the Alfredo sauce and sprinkle with the cheese.
Bake for 40 to 50 minutes or until the casserole bubbles and cheese melts and starts to brown.
Remove from oven and let stand for 10 minutes before serving.
