Step 3
Stir sausage, crushed tomatoes, tomato sauce, diced tomatoes, tomato paste, oregano, basil, rosemary, parsley, black pepper, and red pepper flakes into onion-zucchini mixture. Bring to a simmer, reduce heat to low, cover the saucepan with a lid, and cook, stirring occasionally, until flavors blend and sauce is thickened, about 2 hours.