Boil the pasta according to package directions.
Thaw and warm the meatballs in the microwave, 5-6 minutes total.
In a large skillet, cook the onion till tender.
Add the canned tomatoes, tomato sauce, Hidden Valley Ranch Dressing Mix. Stir until combined.
Stir in the meatballs and continue to heat until pasta is done.
Combine sauce and meatballs with pasta. Top with cheese and serve.