Heat a large pot over medium heat and add the chopped onion.
Sauté the onion until translucent, about 5 minutes.
Add the minced garlic and cook for another minute.
Stir in the diced bell pepper and cook for 3 minutes.
Add the chili powder, cumin, salt, and pepper, mixing well.
Pour in the canned tomatoes and vegetable broth.
Add the black beans and kidney beans, stirring to combine.
Bring the mixture to a boil, then reduce heat to low.
Simmer the chili for 20 minutes, stirring occasionally.
Adjust seasoning if needed and serve hot.