In a small bowl, mix 1/4 cup of mayonnaise with 1 tablespoon of sriracha until well combined, creating a creamy spicy mayo. Shred 8 ounces of imitation crab meat and fold it into the spicy mayo until fully coated. Slice 1 medium cucumber into thin strips.

Lay a bamboo sushi mat on your countertop and place a sheet of nori, shiny side down, on it. With wet hands, spread 3/4 cup of cooked and cooled sushi rice evenly over the nori. In the center, spoon 1/4 of your crab salad and add cucumber strips.

Firmly roll the sushi away from you, sealing the nori with a touch of water along the edge. Wrap tightly in plastic wrap and allow to rest for about 10 minutes.

Carefully unwrap the sushi and slice it into 8 even pieces with a sharp, wet knife. Arrange the sliced rolls on a platter and sprinkle sesame seeds on top if desired.

Serve with soy sauce, pickled ginger, and wasabi for dipping.