In a large non-stick skillet over medium heat combine ground beef, garlic, celery and onions. Cook until vegetables are tender and meat is no longer pink. Add Chilli powder, oregano, an cayenne; cook 1 minute longer. With a slotted spoon, transfer mixture to slow cooker.
Add tomatoes (with juice) kidney beans, cocoa, sugar, cloves, vinegar and pepper, stir to combine. Cover and cook on low for 6-8 hours or on high for 3-4 hours until hot and bubbling. Add green pepper and stir to combine. Cover and cook 20-25 minutes longer. Season to taste with salt and pepper.