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