Step 1: In a large skillet or Dutch oven, heat the olive oil over medium-high heat. Add the ground beef and cook, breaking it up with a spoon, until fully browned. Drain off any excess fat.
Step 2: Add the chopped onion and bell pepper to the same skillet (no need to clean it). Sauté for 5-7 minutes until the vegetables are softened. Stir in the minced garlic and cook for another minute until fragrant.
Step 3: Transfer the browned beef and sautéed vegetables to your slow cooker.
Step 4: Add the diced tomatoes (undrained), crushed tomatoes, rinsed and drained kidney beans, rinsed and drained black beans, beef broth, chili powder, cumin, smoked paprika, dried oregano, unsweetened cocoa powder, salt, and black pepper to the slow cooker.
Step 5: Stir all the ingredients together until well combined.
Step 6: Cover the slow cooker and cook on LOW for 6-8 hours, or on HIGH for 3-4 hours, or until the chili is hot, flavorful, and the flavors have melded together beautifully. The longer it cooks on low, the more developed the flavors will be.
Step 7: Before serving, taste and adjust seasonings if necessary. Add more salt, pepper, or a pinch of cayenne for extra heat if desired.