Heat the olive oil in a large heavy-bottomed pot over medium heat.
Add the chopped onion and cook for 4–5 minutes until softened.
Add the minced garlic and diced red bell pepper. Cook for another 2–3 minutes.
Add the ground beef and cook for 6–8 minutes, breaking it apart with a wooden spoon until browned.
Stir in the tomato paste and cook for about 1 minute.
Add the chili powder, cumin, smoked paprika, oregano, ground coriander, salt, black pepper, and red chili flakes if using.
Stir well and cook for about 30 seconds to release the aroma of the spices.
Add the chopped tomatoes, beef broth, Worcestershire sauce, sugar if using, and bay leaf.
Stir everything together and bring the mixture to a gentle simmer.
Reduce the heat to low, cover partially, and simmer for 25–30 minutes, stirring occasionally.
Add the kidney beans and continue cooking for another 10–15 minutes until the chilli becomes thick and rich.
Taste and adjust the seasoning as needed. Remove the bay leaf.
Serve hot with cooked rice and your favorite toppings such as sour cream, grated cheddar, fresh coriander, and lime wedges.