Preheat oven to 350° and spray a 3 quart casserole dish with a non stick spray. Set aside.
Spoon 2 tablespoons of grease back to pan, add chopped onions and garlic and saute until onions are translucent.
Pour diced tomatoes into skillet with the onions and garlic.
Add Italian sausage back to skillet and bring to a boil.
Cover and simmer on low for approximately 20 - 30 minutes, stirring occasionally.
Drain, rinse and place pasta back in pan.
Place 1/2 of the meat and pasta mixture into prepared casserole dish, sprinkle with cheese, add the rest of the meat and pasta, top with remaining cheese, cover with foil bake until cheese is bubbly and heated through, approximately 30 minutes. Can remove foil and bake the cheese a bit more.
Serve with salad and garlic bread.