Preheat oven to 400 degrees F (200 degrees C). Line a baking sheet with aluminum foil.
Place cream cheese, egg yolk, 1 tablespoon bread crumbs, green onion, lemon juice, Worcestershire sauce, garlic powder, salt, and pepper in the bowl of a mixer. Mix until smooth and evenly blended. Fold in the snow crab and shrimp. Stuff the mushrooms with this mixture, and press into the remaining bread crumbs to coat. Place onto baking sheet stuffing-side-up once coated.
Bake in preheated oven until the mushrooms have softened slightly, 12 to 14 minutes. Set oven to Broil, and broil mushrooms for a few minutes until the tops are golden and bubbly.
