Cut the bagel in half.
Spread butter on the cut side of the bagel and lightly toast it in a pan.
Wash the lettuce and remove excess water.
Thinly slice the tomato and onion.
Place the lettuce on the bottom half of the bagel.
Add slices of turkey breast.
Add the sliced tomato and onion.
Place cheese on top.
Drizzle your preferred sauce.
Cover with the top half of the bagel to finish.