Heat oil in a non-stick pan over medium heat. Sauté the green pepper and onion until soft, (approximately 5-6 minutes). Add in the chopped beef, butter, and steak seasoning; sauté until browned; season with salt to taste.
Spread the cheese on one flatbread, then spread the beef and top with more cheese, cover with another flatbread.
Lightly grease the panini grill with non-stick spray. Cook until golden brown and the cheese is melted. (can also use a non-stick pan over medium heat)
Cut into quarters and serve with pickles and chips. Serve with mustard or your favorite condiments.