Heat the olive oil in a large pot over medium heat. Add the ground beef and cook until browned, breaking it up with a spoon as it cooks.
Add the diced onion, minced garlic, and chopped bell pepper to the pot. Cook for 4 to 5 minutes until the vegetables soften.
Stir in the chili powder and cumin. Cook for 1 minute to toast the spices.
Pour in the diced tomatoes, tomato sauce, and beef broth. Add the drained kidney beans, black beans, and pinto beans.
Season with salt and black pepper. Bring the mixture to a simmer, then reduce the heat and cook uncovered for 25 minutes, stirring now and then, until the chili thickens.
Ladle into bowls and top with shredded cheddar cheese and sliced green onions.