Heat olive oil in a large pot over medium heat. Add onions and cook until translucent, about 5 minutes.
Add garlic and cook for another minute, until fragrant.
Season brisket cubes with salt and pepper, then add to the pot. Cook until browned on all sides.
Stir in chili powder, cumin, smoked paprika, oregano, and cayenne pepper. Cook for 2 minutes to allow the spices to bloom.
Pour in crushed tomatoes and beef broth. Bring to a simmer.
Add kidney beans and black beans. Stir to combine.
Reduce heat to low, cover, and let simmer for 2 hours, stirring occasionally.
Season with additional salt and pepper to taste.
Serve hot, garnished with shredded cheddar cheese, sour cream, and chopped green onions.