Prepare the Mushrooms
Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper. Clean the mushrooms by gently wiping them with a damp paper towel. Remove the stems and set the mushroom caps aside.
Make the Filling
In a mixing bowl, combine the crab meat, cream cheese, Parmesan cheese, mayonnaise, parsley, green onion, lemon juice, garlic powder, salt, and pepper. Mix until well combined and creamy.
Stuff the Mushrooms
Spoon the crab filling into each mushroom cap, pressing gently to secure the filling. Place the stuffed mushrooms on the prepared baking sheet.
Top with Breadcrumbs
Sprinkle a small amount of panko breadcrumbs on top of each stuffed mushroom for added crunch, if desired. Lightly spray or drizzle the tops with olive oil to help them brown.
Bake
Bake in the preheated oven for 18-20 minutes, or until the mushrooms are tender and the filling is golden and bubbly.
Serve
Remove from the oven and let cool for a minute before serving. Transfer to a serving platter and garnish with extra parsley if desired.