Slice cucumber into thin strips and add 1 tablespoon of salt, 1 tablespoon of vinegar, and 2 tablespoons of stevia; let it sit for 10 minutes, then squeeze out the moisture.
Drain the oil from the canned tuna.
Mix multigrain rice with salt, sesame oil, and crushed sesame seeds.
Cut seaweed sheets into four pieces.
Layer seaweed > rice > cucumber > tuna > drizzle sauce and roll up.