Make the rice

1. If using a pot: Rinse and drain the rice a few times until the water runs clear. Combine the rice with water in a medium-sized pot and bring it to a boil over high heat. Reduce the heat to low, cover the pot, and simmer for 15-20 minutes.
2. If using a rice cooker: Rinse and drain the rice a few times until the water runs clear. Combine the rice with water in the rice cooker and cook until the rice cooker signals finished.

Make the Teriyaki Tofu:

1. Cut the tofu into rectangular pieces. 
2. Combine the soy sauce, mirin and sugar to make the Teriyaki sauce.
3. Fry the tofu pieces until golden brown and crispy on both sides, then pour the Teriyaki sauce and simmer on low heat and flip occasionally until most of the sauce has evaporated.

Assemble the Sushi Sandwich:

1. To assemble the Onigirazu, place a sheet of nori on a flat surface with the shiny side facing down. Spread a layer of sushi rice on top of the nori, in a square shape.

2. Layer the teriyaki tofu, avocado, cucumber, and carrot on top of the rice.

3. Add another layer of sushi rice on top of the fillings, pressing down gently to compact the ingredients. Add the sesame seeds and vegan sriracha mayo.

4. Fold the sides of the nori over the filling, then fold the bottom of the nori over the filling and tuck it in tightly. Repeat with the other sheets of nori and filling ingredients. Transfer the Onigirazu to parchment paper or plastic wrap to close.

5. Use a sharp knife to cut the Onigirazu in half.

6. Serve the Onigirazu with soy sauce or any other dipping sauce of your choice.