Rinse the sushi rice under cold water until clear. Cook with water, then mix in vinegar, sugar, and salt after cooking. Let cool.

Cover sushi mat with plastic wrap. Prepare a bowl of water mixed with rice vinegar and gather fillings.

Place nori on the mat, spread rice, and flip it. Layer fillings across the center.

Roll tightly using the mat. Shape into a firm cylinder without squishing too much.

Brush with sauce and sprinkle with breadcrumbs or onions. Press lightly to secure.

Slice into 8 pieces with a wet knife and serve on a platter, optionally drizzled with sauce.