Cook pancetta in a skillet over medium heat until done on both sides. They won’t appear crispy upon taking them out of the skillet, but let them sit for about 2 minutes, and they will be perfect – dainty little crunchy nibbles.
Toast delicious whole wheat bread until crispy and crusty (but not burnt).
Spread a bit of mayonnaise (and mustard if you like) over each slice.
Arrange a layer of arugula leaves, slices of mozzarella (not melted, but you might want to try that version – could be delicious!) pancetta and slices of tomato. Voila!