If the rice isn't fresh, heat in the microwave until hot. Add rice vinegar and sugar and stir together.
Line an 8x8 dish with a plastic cling wrap and press the seasoned rice tightly to pack evenly into the pan.
Cover with the cling wrap and chill in the refrigerator for at least 3 hours. To cut down on time, you can freeze for 30 minutes-1 hour.
While the rice is chilling, prepare the spicy tuna by combining all ingredients in a bowl and mixing together. Taste to adjust seasoning. Cover, and set aside in the fridge while you fry the rice.
Carefully remove the rice from the pan, then slice into mini rectangles with a sharp knife. I made 24 rectangles - 6 strips, each cut into 4 pieces.
Heat avocado oil in a thin layer in a pan over medium high heat. Once the oil is sizzling hot, add the rice squares in a single layer without overcrowding the pan. Pan fry for about 3-4 minutes until golden and crispy, then flip gently and repeat.
Remove from the pan and place on a paper towel. Pan fry the rest of the rice squares.
Assemble: Add sliced avocado on top of the crispy rice. Top with about 2 teaspoons of spicy tuna. Sprinkle with sesame seeds, then add a jalapeño slice on top. Enjoy!