Brown Italian sausage in a large skillet over medium-high heat, breaking into small pieces; drain and rinse well.
Spray slow cooker with nonstick cooking spray.
Add cooked sausage and mix in onion flakes, garlic, crushed tomatoes, tomato paste, water, sugar, oregano, basil, fennel seed, salt and pepper until well combined.
Cover and cook on low for 8 hours.
Serve over cooked pasta.
Top with Parmesan cheese, if desired.
Notes
Nutrition information does not include optional topping.
How to turn this into a freezer meal:Cook the ground sausage and diced onion on the stove top and place in a resealable gallon-sized freezer bag or other freezer-safe container. Dump in the remaining ingredients. Let the bag cool down (if still hot from the cooked sausage). Squeeze out as much air as possible and seal bag closed. Place in the freezer for 60-90 days. When ready to use, dump ingredients from bag into slow cooker. Place the lid on top and cook on LOW heat for 8-9 hours (or until completely heated through - every slow cooker will be a little different). Follow the rest of the instructions as written.