How about cold new potatoes (you can even buy them in cans, so very easy to put together in the mornings!) sliced and diced, with salad dressing (low fat or regular, depending on your tastes there) and some beans or canned tuna? You could chuck in some chopped celery and cucumber for crunch, and grated cheese or whatever for extra flavour & protein.
Variations on this work really well for me, sandwiches never seem that filling, and just make me crave more bread... :sigh: