In a medium skillet, cook the ground beef, sausage, chopped onion, and minced garlic until the meat is brown and the onion is tender, stirring occasionally, about 10 minutes
Meanwhile, prepare the rest of the vegetables by chopping the mushrooms and green pepper
Place the tomatoes, tomato sauce, mushrooms, green pepper, and seasonings in the slow cooker
Stir in the cooked meat mixture
Cover and cook on low for 10-12 hours or high for 5-6 hours