Preheat the oven to 375˚F (190˚C). In an oven-safe baking dish that is large enough to hold about 3½-cup of food. Lightly rub or brush the baking dish with a thin layer of vegetable oil. Set aside.
Separate the imitation crab meat with your hands. If the crab meat is too long, cut them into smaller pieces. Place them in a large bowl. Add 5 tablespoon mayo. Mix well. Set aside.
In a small bowl, combine 1½ tablespoons mayo with sriracha. Set aside.
To assemble, add the hot cooked rice in the prepared baking dish and pat down lightly. Smooth out the top. Let the rice cool for about 5 minutes. Sprinkle a layer of furikake on the rice. Then, place the avocado slices in a single layer (little overlap is ok). Top with the imitation crab. Pack tightly. Gently spread the spicy mayo over the crab.
Bake in the oven for 10 minutes. If you have a broiler, broil for 3 more minutes until lightly golden brown. If you don’t have a broiler, turn up the heat to 450˚F (230˚C) and cook for 5 more minutes until lightly golden brown.
While the sushi is baking, cut the sheets of nori into smaller squares.
Remove from oven. Drizzle the soy sauce over and sprinkle with another layer of furikake. Serve the dish family-style. Scoop a little bit onto a piece of nori, wrap it like a sushi roll & eat.