Preheat your oven to 450°F (230°C).
In a pan over medium heat, sauté the spinach, parsley, onion, and garlic until the spinach wilts and the mixture is well combined. Remove from heat.
In a mixing bowl, combine the sautéed mixture with breadcrumbs, Parmesan cheese, melted butter, Worcestershire sauce, salt, and pepper. Stir until everything is evenly mixed.
Place the shucked Mahurangi oysters on a baking dish.
Spoon the breadcrumb mixture evenly over each oyster, covering it generously.
Bake in the preheated oven for about 10-12 minutes or until the topping is golden brown and the oysters are cooked through.
Remove from the oven and let them cool for a minute before serving.