Stir fry peppers, onion, garlic, parsley and chili powder until onion is clear of color, stir in tomatoes and drain. In a large skillet, heat oil and cook round steak, several slices at a time, turning until browned. Arrange steak on toasted buns and top with cheese (if using Velveeta cut in slices). Broil 4 inches from heat just until cheese melts. Top with tomato mixture and serve.