Heat a large skillet over medium-high heat. When it is hot, add the olive oil and the onion. Cook, stirring occasionally, until the onion is soft.
Add the ground beef and cook, breaking up the chunks, until partially browned.
Add the green bell pepper, garlic powder, salt, and pepper. Stir well and continue to cook the beef.
While the beef is cooking, mix the ketchup, mustard, tomato paste, brown sugar, Worcestershire sauce, soy sauce, and beef broth together in a bowl or glass measuring cup. Then pour into the beef mixture and stir well.
Partially cover the pan and reduce heat to low. Cook for another 10-15 minutes, or until thickened, stirring occasionally.
If you want the buns toasted, place them under the broiler on a baking sheet until both sides are lightly toasted.
Spoon some meat mixture onto the buns are serve hot.