Prepare the Mushrooms:
Preheat your oven to 375°F (190°C).
Gently remove the stems and gills from the portobello mushrooms, creating a cavity for the stuffing. Place the mushrooms on a large baking sheet, stem-side up.
Make the Crab Filling:
In a mixing bowl, combine the crab meat, cream cheese, Parmesan cheese, mozzarella cheese, breadcrumbs, green onions, Dijon mustard, garlic powder, lemon juice, salt, and pepper. Stir until the mixture is well-combined and creamy.
Stuff the Mushrooms:
Spoon the crab mixture into the mushroom caps, packing it in gently but firmly. Be generous with the filling, as it will bake down a bit.
Bake the Mushrooms:
Drizzle the melted butter over the stuffed mushrooms.
Place the mushrooms in the oven and bake for 20-25 minutes, or until the mushrooms are tender and the filling is golden and bubbly.
Serve and Enjoy:
Remove the mushrooms from the oven and allow them to cool slightly before serving. They’re great on their own or served with a fresh salad or side dish.