In a large skillet over medium heat, heat oil. Cook onion until soft and translucent, about 5 minutes. Stir in tomato paste and garlic and cook until fragrant, about a minute more. Add ground beef, season with salt and pepper, and cook until no longer pink, 6 to 8 minutes.
Reduce heat to low and stir in tomato sauce, ketchup, Worcestershire, apple cider vinegar, and brown sugar. Let simmer until slightly thickened, 5 to 7 minutes.
To a large baking dish, add peppers. Divide the mixture evenly into 8 pepper halves and top with cheese. Pour beef broth into baking dish (to help peppers steam) and cover with foil.
Bake until peppers are tender, about 45 minutes. Uncover and broil until cheese is golden, 2 minutes.
Garnish with green onions and serve immediately.
Recipe by Slim Pickins at https://www.slimpickins.org/2018/09/07/sloppy-joe-stuffed-peppers/