In a large skillet over medium heat, cook the ground beef or turkey until browned. Drain excess grease, if necessary.
Add the diced onion, minced garlic, and bell pepper to the skillet. Cook for about 5 minutes until the vegetables are softened.
Transfer the cooked meat and vegetables to the crockpot.
Add the black beans, kidney beans, diced tomatoes, tomato sauce, chili powder, cumin, smoked paprika, salt, black pepper, cayenne pepper (if using), and broth to the crockpot.
Stir all the ingredients together until well combined.
Cover the crockpot and cook on low for 6 hours or on high for 3 hours.
Once cooking is complete, stir the chili and taste for seasoning, adjusting if necessary.
Serve the chili hot, optionally topped with shredded cheese, sour cream, or chopped green onions.