Heat heavy large skillet over medium-high heat. Add beef and cook until brown, breaking up beef with fork, about 6 minutes. Add chopped onion and garlic and cook until onion is transparent, stirring frequently, about 5 minutes. Stir in cumin and cook 1 minute. Add beans, broth and chilies and cook until beans are creamy and thickened, crushing beans with back of spoon, about 15 minutes. Mix in green onions.
Transfer beans to baking dish. Serve with tortillas, cheese, cilantro and salsa, allowing diners to assemble their own burritos at the table. Serves 8.