Rinse the sushi rice thoroughly under cold water until the water runs clear. Cook the rice according to the instructions on the package or using a rice cooker.
While the rice is cooking, prepare the sushi vinegar mixture. Heat the rice vinegar, sugar, and salt in a small saucepan over low heat until the sugar and salt dissolve. Set the mixture aside to cool.
Once the rice is cooked, transfer it to a large bowl and allow it to cool slightly. Pour the sushi vinegar mixture over the rice and gently fold it in using a wooden spoon or rice paddle. Be careful not to crush the rice. Moisten your hands with water and divide the rice into four equal portions. Shape each portion into a round or rectangular rice patty, about one inch thick. Set them aside.
In a small bowl, combine mayonnaise, sriracha sauce, and chopped scallions to create a spicy mayo. Add the cubed salmon to the mayo-sriracha mixture and toss gently until the salmon is evenly coated. Let the mixture sit for a few minutes to allow the flavors to blend.
Prepare three shallow bowls or plates. Place all-purpose flour in one, beaten eggs in another, and breadcrumbs in the third.
Dip each rice patty triangle into the flour, coating it evenly and shaking off any excess. Then dip it into the beaten eggs, allowing any excess egg to drip off. Finally, coat it in the breadcrumbs, pressing gently to ensure a good coating.
Heat oil in a deep fryer or a deep saucepan to around 350°F (175°C). Make sure there is enough oil to submerge the rice patties. Carefully lower the coated rice patty into the hot oil using a slotted spoon or tongs.
Fry them for about 1-2 minutes on each side or until they turn golden brown and crispy. Then take them out and place them onto the plate lined with paper tower.
Arrange some lettuce leaves on top of the rice patty. Then place the salmon-mayo mixture and avocado. Take another rice patty and place it on top of the fillings. Gently press down to secure the burger. Garnish with mixed sesame seeds. Enjoy!