Preheat oven to 375 degrees F. Line a baking sheet with foil for easy clean up if desired.
Remove stems from mushroom caps and use a small spoon to scoop out the hole, making a cavity for the filling to sit in. Discard the stems and extra filling. Place the mushroom caps on the baking sheet, open-side facing up.
Make the creamy crab filling by combing the crab meat, cream cheese, kewpie mayo, soy sauce, green onions, sriracha (if desired) and garlic powder in a bowl. Once combined, scoop the filling into each of the mushrooms, diving the mixture evenly between them.
Bake the mushrooms for 15 to 18 minutes, until moisture begins to release from the bottom of the mushrooms and the filling is slightly golden brown on top. Enjoy the mushrooms while they're nice and warm.
Notes
If your mushrooms are really large, they may take longer to bake. If they are on the smaller side, you can get more mushrooms filled with the amount of filling this recipe makes.