Preheat the oven to 350°. Rinse sushi rice in a fine mesh strainer until the water runs clear; drain well. Add rice, 1-1/2 cups water and salt to a large saucepan. Bring to a boil; reduce heat to low. Cover; simmer 20 minutes. Remove from the heat; let sit, covered, for 10 minutes. Fluff rice with a fork; stir in sugar and rice vinegar.
Meanwhile, in a large bowl, combine crab, 1/4 cup mayonnaise and wasabi, if using.
Firmly press the cooked sushi rice into the bottom of a 9x9-in. baking pan. Spread the crab mixture evenly over the rice. Bake 10-15 minutes or until heated through.
Meanwhile, in a small bowl, combine cucumbers, soy sauce and sesame oil; set aside.
Heat olive oil in a small skillet over medium heat. Once the oil begins to shimmer, add panko bread crumbs. Toast 1-2 minutes or until lightly golden; transfer to a plate.
In a small ramekin, combine Sriracha and remaining 2 tablespoons mayonnaise; set aside.
To assemble, spread mashed avocado over the crab mixture, scatter with marinated cucumbers and sprinkle with toasted bread crumbs. Drizzle with Sriracha mayo and sprinkle with green onion and furikake. Serve immediately.