Prepare the rice: In a small bowl, mix rice vinegar, sugar, and salt until dissolved. Pour over freshly cooked sushi rice and gently stir.
Shape and chill: Line a baking pan with plastic wrap and press the seasoned rice into an even layer. Cover and refrigerate for at least 4 hours or overnight until firm. Cut into 16 equal rectangles.
Make the spicy salmon: In a bowl, combine chopped salmon, Kewpie mayo, sriracha, soy sauce, scallions, and sesame oil. Stir well, cover, and refrigerate.
Fry the rice: Heat vegetable oil in a skillet over medium heat. Fry the rice rectangles in batches until golden brown and crispy on both sides. Transfer to a paper towel-lined plate.
Assemble: Top each crispy rice piece with a slice of avocado, a scoop of spicy salmon, and a jalapeño slice. Sprinkle with sesame seeds.
Serve immediately and enjoy!