In a large pot, brown the ground beef over medium heat until fully cooked.
Drain excess fat and return beef to the pot.
Add chopped onion and minced garlic; sauté until soft.
Stir in chili powder, cumin, salt, and pepper; cook for 1 minute.
Add diced tomatoes, tomato sauce, and beef broth; mix well.
Incorporate kidney and pinto beans into the mixture.
Bring the chili to a boil, then reduce heat to low.
Cover and let simmer for 30 minutes, stirring occasionally.
Adjust seasoning to taste, adding more chili powder if desired.
Serve hot, garnished with shredded cheese and green onions if using.