Heat olive oil in a large pot over medium heat.
Add chopped onion and bell pepper; sauté until soft.
Stir in minced garlic and cook for 1 minute.
Add diced tomatoes and mix well.
Incorporate black beans, kidney beans, and corn.
Sprinkle in chili powder, cumin, salt, and pepper.
Stir the mixture thoroughly to combine all ingredients.
Bring to a simmer, then reduce heat to low.
Cover and cook for 20 minutes, stirring occasionally.
Taste and adjust seasoning if needed.