Preheat the oven to 350°F and spray a baking dish large enough to hold 12 mushrooms with nonstick spray.
Remove the stems from 12 large mushrooms and clean them with a dry paper towel.
In a mixing bowl, stir together 1 can (6 oz) drained minced clams, 1 chopped green onion, 1 beaten egg, 2 teaspoons minced garlic, ½ cup Italian bread crumbs, 1 teaspoon dried oregano, 1 tablespoon melted butter, and 3 tablespoons grated Parmesan cheese.
Spoon 1–2 tablespoons of the filling into each mushroom cap and place them filling-side up in the baking dish.
Drizzle 3 tablespoons melted butter over the stuffed mushrooms.
Cover the dish with foil and bake for 20–30 minutes until the mushrooms are tender.
Remove the foil and sprinkle ¼ cup finely grated mozzarella cheese over the mushrooms.
Bake uncovered for 2–3 minutes until the cheese is melted.
Serve warm and enjoy.
Notes
These are best served fresh but you can refrigerate the leftovers for up to 3 days. Reheat in the oven or air fryer to make them heated through and slightly crispy again.