Preheat oven to 350 degrees.
Sautee onions and garlic in olive oil, until soft.
Add ground beef and season with salt and pepper
Once the beef is cooked through, stir in tomatoes and tomato sauce.
Stir in uncooked tortellini and 1.5 cups of the mozzarella cheese.
Transfer to the casserole dish and sprinkle the remaining cheese over the top.
Cover tightly with foil and bake for 30 minutes.
Remove from oven sprinkle on a little basil, or parsley.
Serve with a side salad and breadsticks