In a medium mixing bowl, combine the softened cream cheese, lump crab meat, green onions, garlic powder, onion powder, and half of the parmesan cheese. Use a spatula or fork to mix everything together until the ingredients are well incorporated. Season with a small pinch of salt and black pepper, keeping in mind that the cheese and crab already provide a natural saltiness.
Using a small spoon or a piping bag, generously fill each mushroom cap with the crab and cream cheese mixture. Press the filling down slightly to ensure it is packed well, then mound a little extra on top for an attractive look. Place the stuffed mushrooms onto the prepared baking sheet, leaving a small amount of space between each one.
In a small bowl, toss the Panko breadcrumbs with the remaining parmesan cheese, chopped parsley, and melted butter. Sprinkle a pinch of the crumb mixture over the top of each stuffed mushroom. Place the baking sheet in the oven and bake for 18 to 20 minutes, or until the mushrooms are tender and the breadcrumb topping is a beautiful golden brown. Serve while warm.
