Prepare Rice: Begin by making a batch of seasoned sushi rice. Let it cool to room temperature before starting the vegan tuna rolls. Peel Tomatoes: Bring a large pot of water to a boil. Using a sharp knife, make a small "x" mark on the bottom of each roma tomato.
Place the tomatoes in boiling water and cook for 1-2 minutes or until the skin begins to peel off slightly. Be careful not to overcook. Immediately transfer the tomatoes to a bowl of cold water with ice cubes to stop the cooking process.
Once cooled, carefully peel off the tomato skin and cut into quarters, remove the seeds and inner flesh and cut further into thin strips about 1/2 inch wide.
Marinade Tomatoes: In a bowl, mix soy sauce, mirin, nori (cut with scissors into small pieces), sesame oil, and liquid smoke. Add tomatoes and coat evenly. Marinate for 30 minutes to an hour.
Assemble Rolls: Wrap the bamboo mat in plastic wrap; this prevents the rice from sticking to the mat and makes clean-up easier. Cut the whole nori sheet in half using scissors to make two half sheets.
Place a half sheet of nori horizontally on your bamboo mat, shiny side down, rough side facing up. Wet your fingers in water and grab sushi rice (about 1/2 - 2/3 cup). Spread evenly on the nori, leaving 1/2 inch at the top uncovered. Add a single layer of your marinated tomatoes, about 3 slices, in the center of the rice.
To Roll The Sushi: Lift the edge of the bamboo mat closest to you and fold it over the tomato filling. Hold the filling with your fingers and apply light pressure to tighten the roll.
Wet the uncovered nori with water to act as glue, then lift the sushi mat and roll the sushi to seal it completely. Press firmly with both hands to shape the roll.
Cut the roll in half with a damp, sharp knife. Then, slice each half into thirds for 6 pieces using a back-and-forth motion. Dip the blade in water before each cut and wipe it clean after each slice. Finish by garnishing with a dot of sriracha.