In a large pot over medium heat, heat the oil. Add the onions, garlic, and red pepper; cook, stirring frequently, until softened, 4 to 6 minutes. Add the beef and increase the heat to high; cook, stirring with wooden spoon to break the meat into 1/4-inch pieces, until the beef is browned, 10 to 12 minutes. (The beef will release a lot of liquid — do not drain it; you’ll skim the fat off at the end.)