Preheat oven to 350 degrees. Place custard cups or muffin pan on a cookie sheet (this allows you to move the pan in and out safely)
Place 2 ham slices over an inverted oven-proof custard cup or muffin pan (in an x-shape works best for perfect coverage).Place second custard cup over the first (to protect ham from overcooking).
Cut excess ham from bottom, leaving 1.2″ or so (ham will shrink during cooking, but tips can burn if too much is left).
Bake for 20 minutes. Carefully remove from oven to cooling rack. Remove top bowl to cool, bottom bowl once bowl is cool enough.
Fill with shredded lettuce, chopped egg, tomato and shredded cheese. Serve cold.