Rinse 2 cups sushi rice in a fine-mesh strainer under cold water until the water runs clear, about 1–2 minutes; drain thoroughly.
Combine the rinsed rice and 2 1/4 cups water in a saucepan and bring to a simmer over medium-high heat with the lid on; reduce heat to medium-low and simmer gently for 16–18 minutes, until the liquid is absorbed.
Remove the pan from heat and let the rice steam, covered, for 10 minutes without lifting the lid.
While the rice cooks, heat 1/4 cup rice vinegar with 4 teaspoons sugar and 1 teaspoon fine sea salt in a small saucepan until very warm but not boiling, stirring until the sugar dissolves; remove from heat.
Transfer the hot rice to a large bowl, remove the lid, and gently fold in the vinegar mixture with a spatula or fork until evenly coated; cover the rice with a damp towel and let cool.
Whisk together 2 cloves minced garlic, 1 teaspoon grated ginger, 1 tablespoon toasted sesame oil, 2 tablespoons soy sauce, 2 tablespoons honey, and 2 teaspoons sriracha (if using) to make the marinade.
Toss 2 lbs salmon cubes in the marinade to coat; let sit 30 minutes in the refrigerator for best flavor, or proceed immediately.
Heat a large skillet over medium-high heat until hot, add 1 tablespoon canola oil and swirl to coat.
Using tongs, add the salmon cubes (shake off excess marinade) and sear 2–3 minutes per side until browned and cooked through.
Pour any remaining marinade into the skillet, toss with the salmon, and cook 1 additional minute to coat.
Divide the sushi rice among bowls and top with cooked salmon, shredded purple cabbage, cubed pineapple, cubed mango, edamame, shredded carrot, sliced avocado, sliced cucumber, microgreens, sesame seeds, pickled ginger, seaweed, and a drizzle of spicy mayo.
Serve immediately.