Heat about 2 tablespoons olive oil in a non-stick skillet over medium high heat. Cook beef, onion and garlic in the skillet until beef is no longer pink. Drain.
Place beef mixture inside a large slow cooker. Add remaining ingredients and stir to combine.
Cover and cook on LOW for 6-8 hours or on HIGH or 3-4 hours.
Season with salt and pepper, to taste. Garnish with cheese and onion if desired.