Cook the macaroni according to the package directions. Drain and reserve.
Meanwhile, cook the onions and garlic in the olive oil in a large pot over medium until the onions are softened, about 10 minutes. Add the ground beef, salt, and pepper and cook, stirring occasionally, until the meat is browned, about 8 minutes. Stir in the chili powder and ground cumin; cook 2 minutes more. Add the beans, canned tomatoes, and broth. Bring to a boil, reduce heat to a simmer, and cook for 20 minutes.
Stir in the macaroni to warm and serve, garnished with shredded cheddar and sliced scallions, and with corn bread on the side.