Sushi Rice: Add cold water to rice, swish, and drain. Do this a few times until water is no longer cloudy. Add 2 cups of cold water to the rice and set over high heat until water boils. Reduce heat to a gentle simmer and let cook for 15 minutes, covered. Remove from heat, leaving the lid on and not stirring, and let rest for 15 minutes while you prepare the rest of the recipe.
Rice Seasoning: Combine rice vinegar, sugar, and salt in a microwave-safe bowl. Microwave for about 15 seconds then stir to dissolve sugar. Set aside.
Asparagus: Heat oil in a large saute pan over medium heat. Add minced garlic and asparagus, cooking until asparagus is fork-tender.
Prep Fillings: Thinly slice the avocado, cucumber, and bell pepper. Drizzle lime juice over avocado to prevent browning.
Sauce: Combine mayonnaise and sriracha.
Assemble: Drizzle half of the rice vinegar mixture over the rice and stir to incorporate. Sprinkle in the rest and continue stirring. Spoon rice into 2 or 3 serving bowls. Top with cooked asparagus, avocado, cucumber, bell pepper, and a handful of crumbled nori. Serve drizzled with sriracha mayonnaise.
Best enjoyed immediately. Leftovers can be stored in an airtight container in the fridge for 2 to 3 days.