Begin by heating a large skillet over medium heat and adding the lean ground beef and ground chuck. Cook, stirring occasionally, for about 8-10 minutes until the meat is fully browned and no longer pink. Drain any excess fat.

Transfer the browned meat into your slow cooker. Add the tomato sauce, diced tomatoes, tomato paste, chopped onion, and bell pepper. Then, add the minced garlic, cayenne pepper, ground cumin, chili powder, sugar, oregano, salt, and pepper. Stir thoroughly.

Cover the slow cooker and set it to cook on low for 6-8 hours or on high for 4 hours. Avoid lifting the lid during cooking.

After cooking, taste and adjust seasoning if needed. Ladle the hot chili into bowls and top with shredded cheese or sour cream if desired.