A traditional favorite improved by a day’s worth of simmering in your crockpot. I take the short route and start with cans of spaghetti sauce!
If you'd like to shorten prep time, eliminate the Italian sausage. Simply add all ingredients to the crockpot, cover and cook on low 8 hours or high 4 hours. Don't worry about cooking anything in the skillet - your crockpot will take care of it!
Remove casings from sausage (if present), brown in large skillet over medium heat. Drain. Add onion, garlic, green pepper, pepperoni, and mushrooms, simmer 15 minutes. Add to crockpot. Mix in spaghetti sauce, tomatoes, and seasonings, cover and cook on low 8 hours or high 4 hours.