Heat olive oil in a large pot over medium heat.
Add diced onion and garlic; sauté until softened.
Stir in the ground beef; cook until browned.
Add the red bell pepper and cook for another 2 minutes.
Mix in chopped tomatoes and tomato paste.
Stir in kidney beans and spices (chili powder, cumin, salt, and pepper).
Bring the mixture to a simmer and reduce heat.
Cover and cook for 20 minutes, stirring occasionally.
Taste and adjust seasoning as needed.
Serve hot, garnished with cheese or sour cream if desired.