Peel and slice the cucumber lengthwise into strips about 1/8 of an inch wide. Being careful to not damage the avocado, pit and peel the avocado by cutting it in half lengthwise around the pit and sliding the two halves apart, then scoop out the pit and peel off the skin with your fingers. Slice the avocado as thinly as you can while keeping the slices uniform. When sliced, slide the stack of slices onto their side and spread them out in a line like a deck of cards with one side showing. Make the line of avocado the length of one sushi roll.
Fill a small bowl with water and add a tablespoon of rice vinegar. Warm it up for about 20 seconds in the microwave and set it to the side of your rolling station. Wrap a bamboo mat with plastic wrap and cut a sheet of nori (seaweed) in half. Place the nori shiny side down, ridged side up, on the mat. Dipping your fingers in the vinegar water periodically, gently place the sushi rice over the sheet of nori til the sheet is covered by just one or two layers of rice grains. Do not mash the rice onto the sheet, but make sure it just sticks.
Gripping the sheet by two corners, flip the sheet of nori rice side down back onto the bamboo mat. Then put the shrimp tempura, cucumber strips, and tobiko at the bottom of the nori sheet. If you want, put the unagi on as well.
From the bottom end, start rolling the sushi. Hold the edge of the mat with your thumbs and lift the nori and fold it over the filling ingredients. Make sure to keep the ingredients in place and that the rice sticks together. Tuck the front edge of the nori into the roll, and remove the mat as you continue to roll the sushi. Roll slowly so that you ensure that the sushi is coming out even. You will need to tighten the roll to keep ingredients from falling out when you cut it. Remember to tighten the roll with your sushi mat often, but not so tightly that you smash the ingredient. Roll the sush
Using the flat of a wide knife, scoop up your line of avocado and place it on top of the roll. Place a sheet of plastic wrap over the top and then put your bamboo mat over. Tightly squeeze the roll until the avocado slices wrap around the sushi. Be gentle enough to not tear the avocado.
Cut the roll into 8 even pieces with a ridiculously sharp knife. Dip the knife into the vinegar water between each cut to keep it from sticking.
Serve with tobiko on top and drizzle with spicy mayo and unagi sauce.
