Boil water in a large pot over medium high heat. Add the tomatoes and cook until the skin starts to peel/split on the tomato.
Remove the tomatoes and soak in ice bath to stop the cooking. Peel the skin away from the tomatoes when they are cool to touch.
Cut the seedy inside portion out and keep the outer "meaty" parts of the tomato. Dice the meaty chunks into small pieces.*
In a separate bowl, combine mayo, sriracha, sugar, salt, sesame oil, and soy sauce. Toss the tomato pieces in the sauce.
Prepare the sushi rolls by adding a thin layer of rice to a sheet of seaweed.* Leave a 1-2 inch area without rice at the end of the roll to allow for easy rolling later. Layer avocado, tomatoes, and cucumber together and roll the sushi as shown above.
Use a bit of water on your fingers to wet the end of the roll and seal together. Slice and add a dot of unagi sauce to the top of the roll.
When separating meaty tomato portion away from seeds, don't keep any hard parts. It wont be very good in the roll. Make sure you dampen your fingers with water before handling sushi rice so it won't stick to your hands.