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 heat for 15 minutes. Remove from heat and let stand covered for 10 minutes.
02 - Whisk together 2 tbsp rice vinegar, 1 tbsp sugar, and 0.5 tsp salt in a small bowl. Gently fold seasoning into cooked rice and allow to cool to room temperature.
03 - In a medium bowl, whisk soy sauce, sesame oil, sriracha, mayonnaise, rice vinegar, honey, sliced spring onion, and toasted sesame seeds until fully combined.
04 - Add diced tuna to the marinade and toss to coat evenly. Refrigerate for 10-15 minutes to allow flavors to meld.
05 - Dice the mango, slice avocado and cucumber into thin rounds, julienne the carrot, and cut nori sheet into thin strips. Set aside arranged on a platter.
06 - Divide seasoned sushi rice among 4 bowls. Arrange spicy tuna mixture, mango, avocado, cucumber, carrot, and nori strips in sections over the rice.
07 - Sprinkle with black sesame seeds, add pickled ginger and fresh coriander if desired. Drizzle with additional sriracha and serve with lime wedges on the side.