Place all ingredients for the meatballs in a bowl and mix until well combined. Divide meat mixture into two parts and mold them to form two patties. With a shot glass, cut out the middle of each pattie to form the bagel shape.
Arrange bagels onto a baking tray and bake for 20-25 minutes.
When cooked, let sit for 5 minutes. Cut each bagel in half lengthwise, just like a regular bagel, and spread each half with mayo.
Place a lettuce leaf, cheese and tomato slices on each bottom part of the bagel, and season with salt and pepper.