01 - Rinse sushi rice in cold water until water runs clear. Combine rice and water in a saucepan, bring to a boil, then cover and simmer on low for 15 minutes. Remove from heat and let sit, covered, for 10 minutes.
02 - In a small bowl, mix 2 tbsp rice vinegar, 1 tbsp sugar, and 0.5 tsp salt. Gently fold this seasoning into the cooked rice and let it cool to room temperature.
03 - In a medium bowl, whisk together soy sauce, sesame oil, sriracha, mayonnaise, rice vinegar, honey, sliced spring onion, and toasted sesame seeds to create the marinade.
04 - Add diced tuna to the marinade, toss to coat thoroughly, and refrigerate for 10–15 minutes to allow flavors to meld.
05 - Dice the mango, slice avocado and cucumber into thin rounds, julienne the carrot into matchsticks, and cut nori sheet into thin strips.
06 - Divide seasoned sushi rice among 4 bowls. Arrange spicy tuna, mango, avocado, cucumber, carrot, and nori strips decoratively on top of the rice.
07 - Sprinkle with black sesame seeds, add pickled ginger and fresh coriander if desired, drizzle with extra sriracha, and serve with lime wedges on the side.