Fry ground beef on medium-high heat until browned using a wooden spoon or meat chopper.
Add browned meat, onions, seasonings, tomato paste, mushrooms, tomatoes, and pepper to slow cooker.
Cook on high for 4 hours, or low 8 hours (or longer). Serve over cooked spaghetti and garnish with freshly cracked pepper, parsley, and parmesan cheese if desired.
May substitute Italian mix or spaghetti seasoning packet in lieu of seasonings listed in the recipe.May substitute diced tomatoes for canned tomatoes if you prefer, or once sauce is cooked, break up tomatoes with a wooden spoon or meat chopper.