Rinse the sushi rice under cold water until clear. Combine with water in a rice cooker and cook according to instructions. Let rest for 10 minutes.

Mix rice vinegar, sugar, and salt in a saucepan until dissolved. Fold into rice once cooled to enhance flavor.

Finely dice the sushi-grade tuna and combine with mayonnaise, sriracha, sesame oil, and soy sauce. Mix in sesame seeds and green onions.

Slice the avocado and brush with lemon juice to prevent browning.

Prepare tempura batter and heat vegetable oil. Fry panko until golden and crispy, then drain on paper towels.

Spread rice on nori, add tuna mixture and avocado, then roll tightly using the bamboo mat.

Slice the roll into bite-sized pieces and garnish with tempura flakes and sesame seeds. Serve with additional sriracha mayo.