Cover bamboo sushi mat with plastic wrap. Lay a 2/3 nori sheet, shiny side down on the sushi mat.
Wet your fingers with Tezu and spread 3/4 cup sushi rice evenly onto nori sheet.
Turn the nori sheet over so that the rice is facing down. Line the edge of the nori sheet at the bottom of the bamboo mat.
Put two pieces shrimp tempura at the bottom edge of the nori. If desired, add unagi sauce here. Place cucumber and tobiko next to the shrimp tempura.
Grab the bottom edge of the mat while keeping the filling in place with your fingers and roll it into a tight cylinder, tucking the fillings in firmly. Lift the edge of the mat slightly and roll forward will keeping gentle pressure on the mat.
Using the side of a knife, transfer the fanned out avocado to the top of the sushi roll. Place plastic wrap over the roll and gently put the bamboo mat over. Squeeze the roll until the avocado slices wrap around the sushi. Be gentle as to not break the avocado slices.
Wrap the rolls in plastic wrap to keep them from drying out while you make the other rolls.
With a sharp knife, cut each roll into 8 pieces. Keep a single layer of plastic wrap over the rolls while you cut to get a cleaner slice. Also clean your knife after every couple of cuts.
Transfer slices to a serving plate. Top each with tobiko, then a dab of spicy mayo and a sprinkle of toasted black sesame seeds. Place some unagi sauce on the plate so that you can dip the sushi.