In a large bowl, mix the surimi, parsley, scallions, Parmesan cheese, bread crumbs, garlic powder, salt, and pepper. Add the mayonnaise, yogurt, lemon juice, soy sauce, and mustard and mix well. Use a spoon to fill each mushroom with the mixture, gently pressing it into the mushrooms. Bake for 20 minutes, until heated through and the tops begin to brown. Serve hot!