Cut the ends off the cucumber and slice in half lengthwise. Use a y-shaped veggie peeler to slice the cucumber into long thin strips. If your cucumber has a lot of seeds, you may want to discard the first few slices. Stop once the cucumber gets too thin to slice.
In a medium bowl, combine mayonnaise and sriracha. Stir in a can of tuna and sliced green onions. Taste, and adjust heat/salt to your liking.
Lay each slice of cucumber down on a flat surface. Spread tuna salad over the top of each slice, leaving 1" of cucumber at the end without salad. Place a slice of avocado at the end of the cucumber, and roll the cucumber tightly over the avocado. Repeat until you've used up all the cucumber slices, tuna salad, and avocado.
Serve with additional hot sauce, green onions, and sesame seeds. Enjoy!