Press cooled sushi rice firmly into a rectangular baking dish about 1 inch thick. Refrigerate for 15 minutes to firm up, then cut into 8-12 rectangular pieces.

In a bowl, combine diced salmon with 1 tablespoon mayonnaise, 1 teaspoon sriracha, and soy sauce. Mix gently and refrigerate until ready to use.

Heat vegetable oil in a non-stick skillet over medium-high heat. Fry rice cakes for 3-4 minutes per side until golden brown and crispy. Transfer to a paper towel-lined plate.

Mix remaining 2 tablespoons mayonnaise with 1 teaspoon sriracha in a small bowl. Transfer to a squeeze bottle or small plastic bag for drizzling.

Place crispy rice cakes on a serving platter. Top each with a spoonful of spicy salmon mixture and a slice of avocado.

Drizzle spicy mayo over the top, then sprinkle with toasted sesame seeds and sliced green onions. Serve immediately while rice is still crispy.