Add the onion, green pepper, garlic, tomatoes, beans, tomato paste, ketchup, barbecue, mustard, chili powder, and cumin to the crockpot. Stir all the ingredients together until the mixture's combined.
1 large white onion, 1/2 large green pepper, 4 garlic cloves, 2 14 oz cans diced tomatoes, 2 15 oz cans chili beans, 2 tbsp tomato paste, 2 tbsp ketchup, 2 tbsp barbecue sauce, 1 heaping tbsp yellow mustard, 3 tbsp chili powder, 1/2 tsp cumin