Whisk marinara, crushed tomatoes, onion, garlic, Italian seasoning, red pepper flakes, brown sugar, Worcestershire, salt, and pepper in a bowl.
Pour the sauce over the meatballs and toss to coat evenly.
Cover and cook on High for 2.5–3 hours or on Low for 4–5 hours, stirring once halfway.
Stir in parsley. Serve hot with Parmesan sprinkled on top.
Notes
Variation: For a sweet-heat party twist, swap the marinara and crushed tomatoes for 1.5 cups chili sauce and 1.5 cups grape jelly, then reduce brown sugar to 1 tsp.Serving/Storage: Great over buttered noodles or in toasted hoagie rolls. Refrigerate up to 4 days or freeze up to 3 months.This recipe is an original creation inspired by classic Easy Crockpot Meatballs flavors. All ingredient ratios and instructions are independently developed.