I have fixed this a few different ways depending on what I have on hand, I like to make this sandwich w/ fresh mushrooms instead of bell bepper & onion. I also use fat free cream cheese instead of mayo& mozzarella then top w/ handful of sprouts!!
Bell peppers are also great when grilled with the eggplant so feel free to experiment as it is good a lot of ways. So get that grill out and start cooking!