Preheat the oven to 400 degrees. Prepare a 9 x 13 casserole dish with nonstick cooking spray.
Cook the elbow macaroni according to package directions for al dente (less firm). Drain and keep warm.
In a large skillet over medium high heat, add the olive oil, sausage, onion, green bell pepper, and red bell pepper, cook for approximately 6 to 8 minutes or until the vegetables have begun to soften. Remove the sausage and vegetables from the skillet to a plate and keep warm.
To the skillet, add the butter and heat until melted. Stir in the flour and whisk until bubbling. Slowly add the milk, whisking constantly until slightly thickened. Stir in the seasonings and cheeses, allowing the cheese to melt.
Add the sausage and vegetables as well as the elbow macaroni to the cheese sauce. Start until combined.
Transferred to the prepared casserole dish and topped with additional cheese if desired. Bake for 20 to 25 minutes or until the top is browned slightly.