Saute onions in oil over medium-high heat in a 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 the water for pasta. Add cooked meatballs to the sauce and simmer, uncovered, for 10 minutes to heat through. Meanwhile, cook pasta according to package directions, drain. Stir in the cooked pasta and toss well to coat. Before serving, add the fresh basil strips. Garnish pasta and meatballs with grated Parmesan cheese.