n a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Add the tomato sauce, chilies, mushrooms, chili powder, olives and garlic salt. Bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes or until heated through. Add cheese; cook and stir until melted.
Cut 1/4 inches off the top of each roll; set aside. Carefully hollow out bottom of roll, leaving a 1/4-in. shell (discard removed bread or save for another use). Fill each roll with about 1/2 cup meat mixture. Replace bread tops.
Individually wrap four sandwiches tightly in foil; freeze for up to 3 months. Place remaining sandwiches on a baking sheet. Bake at 350° for 10-15 minutes or until heated through.
To use frozen sandwiches: Thaw in the refrigerator overnight. Place foil-wrapped sandwiches on baking sheets. Bake at 350° for 20-25 minutes or until heated through.