In a small saucepan, add the rice vinegar, sugar, and salt. Heat this over high heat until the sugar dissolves. While the cooked sushi rice is still warm, fold this mixture into it.
Line a rectangular dish/tray with plastic wrap. Scoop the rice into it and press into a ½-inch thick rectangle. Cover with more plastic wrap and freeze for one hour, then refrigerate for another hour. Alternatively, you can just refrigerate it 6 hours.
While the rice is refrigerating, lay the tuna on a cutting board and chop it repeatedly until it becomes a fine mince. Transfer to a small bowl with the rest of the spicy tuna ingredients and mix well. Set aside in the fridge until ready to use.
Remove the rice to a cutting board and cut into small rectangles.
Heat ¼ cup of oil over medium-high heat in a nonstick pan (you can also use 2 tablespoons if you're oil-adverse). Add the rice and cook each side for 4-6 minutes until golden brown and crispy. Transfer to a wire rack to drain excess oil. If the heat is too high, reduce to medium heat.
To assemble, lay a few slices of avocado onto the rice, followed by a scoop of tuna and a slice of jalapeno.