All you need to do is cut your bagel in half and spread the mustard on each side.

Now, place the cucumber, lettuce, tomato, and green pepper on one side of the bagel. Be sure to add seasonings of your choice, and include pepper and salt for your tomato.

For the big finale, add the alfalfa sprouts and onions. Now, just place the other half of the bagel onto the layered half and serve.