You can use different types of bread!
In a bowl, mix tuna, Greek yogurt, 1.5T lemon juice, 1T allulose, sweet corn, and pepper together.
Place the heated and halved bread on plastic wrap, and pile the previously prepared mixture onto one side.
Top with shredded onion, shredded cucumber, sliced boiled egg, and halved cherry tomatoes.
In a bowl, make a sauce with 0.5T whole grain mustard, 0.5T allulose, and 0.5T mayonnaise. Spread the sauce on the other piece of bread, place it on top, and wrap the sandwich in the plastic wrap.