In a large skillet over medium heat, brown the ground beef or turkey until fully cooked. Drain any excess fat.
Add the diced onion, garlic, and bell pepper to the skillet. Sauté for about 5 minutes until the vegetables are softened.
Transfer the meat and vegetable mixture to the crockpot.
Add the kidney beans, black beans, diced tomatoes, and beef broth to the crockpot.
Sprinkle the chili powder, cumin, paprika, salt, black pepper, and cayenne pepper (if using) over the mixture. Stir well to combine all the ingredients.
Cover the crockpot and cook on low for 6 hours or on high for 3 hours.
Once done, give the chili a good stir, taste, and adjust seasonings if necessary. Serve hot.