Step 1: In a large skillet, brown the ground beef over medium-high heat. Break it up with a spoon as it cooks. Once fully browned, drain off any excess grease and transfer the beef to the slow cooker.
Step 2: Add the chopped onion, bell pepper, and minced garlic to the slow cooker with the browned beef. Stir gently to combine.
Step 3: Add the diced tomatoes (undrained), tomato sauce, tomato paste, and beef broth to the slow cooker.
Step 4: Stir in the rinsed and drained kidney beans and black beans.
Step 5: Add the chili powder, ground cumin, dried oregano, smoked paprika, cayenne pepper (if using), salt, and black pepper to the slow cooker. Stir all ingredients thoroughly to ensure everything is well combined and coated with spices.
Step 6: Cover the slow cooker and cook on LOW for 6-8 hours or on HIGH for 3-4 hours, or until the chilli is heated through and flavors have melded.
Step 7: Before serving, taste the chilli and adjust seasonings as needed. If desired, add a pinch of sugar to balance acidity or more salt/pepper/chili powder for taste.
Step 8: Ladle the hot chilli into bowls and serve with your favorite toppings such as shredded cheese, a dollop of sour cream, chopped green onions, fresh cilantro, or diced avocado.