Saute onions & mushrooms in olive oil over med-high heat in large pan until translucent, about 4 minutes
Stir in garlic. Cook just until you smell it, about 30 seconds.
Add tomatoes, pan drippings, parsley, sugar, pepper flakes, and salt. Simmer 15 minutes. Start boiling water for pasta.
Add cooked meatballs to the sauce & simmer uncovered for 10 minutes to heat through.
Cook pasta according to package directions, drain.
Stir in the cooked pasta & toss to coat
Garnish pasta & meatballs with grated parmesan cheese