Combine Italian dressing, onion, and green pepper in a small saucepan; bring to a boil. Reduce heat, and simmer, uncovered, until onion is tender. Set aside to cool.
Scoop out bottom half of each roll, leaving a 1/2-inch shell. Discard excess bread. Spread mustard evenly in bottoms of rolls. Top with pastrami, onion mixture, cheese, pepperoncini peppers, and ham. Spread mayonnaise evenly on cut sides of top halves of rolls; place on top of the bottom halves of rolls. Wrap each roll in aluminum foil, and place on a baking sheet. Bake at 375° for 15 minutes or until thoroughly heated.