Stir together the mayo and Sriracha in a small bowl. Cover and chill until ready to use.
In a bowl, hand-whisk together all Sauce ingredients. Stir cubed tuna into the sauce, coating well. Cover and keep chilled until ready to assemble bowls.
Divide cooked rice into desired amount of bowls. Evenly layer each bowl according to order: lettuce, marinaded tuna/salmon, cucumber, carrot, and avocado. Sprinkle with chopped cilantro, green onions, and sesame seeds as desired. Drizzle with Sriracha Mayo. Serve immediately.