Heat the olive oil in a large skillet over medium heat. Add the onions and bell peppers and saute until softened, about 10 minutes. Add the beef, breaking it up with a wooden spoon, and cook until browned, 3 to 5 minutes. Add the tomatoes, beans, tomato paste, vinegar, brown sugar, and some salt and pepper, and cook until slightly thickened, 10 to 15 minutes.