01 - In a large skillet over medium-high heat, brown beef cubes on all sides, about 5 minutes. Transfer to the slow cooker.
02 - Add diced onion, red bell pepper, garlic, and jalapeño to the skillet. Sauté 2–3 minutes until softened. Transfer to the slow cooker.
03 - Add kidney beans, black beans, diced tomatoes, tomato paste, and beef broth to the slow cooker.
04 - Sprinkle chili powder, cumin, smoked paprika, oregano, cayenne (if using), salt, and black pepper into the slow cooker. Stir to combine.
05 - Cover and cook on low for 6–8 hours or on high for 4 hours until beef is tender and flavors meld.
06 - Taste and adjust seasoning as needed before serving.
07 - Serve hot with optional toppings such as cilantro, sour cream, shredded cheddar cheese, or sliced green onions.