Preheat oven to 375°F and grease a 2-quart baking dish with butter or nonstick spray. Set aside.

In a large bowl, combine shrimp, mayonnaise, Old Bay seasoning, garlic, and black pepper. Stir until well coated.

Add grated mozzarella and Parmesan to the shrimp mixture. Stir to combine, then transfer mixture to prepared baking dish.

In a small bowl, mix melted butter with panko breadcrumbs. Sprinkle evenly over the shrimp mixture.

Bake for 15–20 minutes, or until shrimp are just cooked through (145°F internal temp) and topping is golden and crisp.

Optional: Broil for 1–2 minutes for a deeper golden crust. Garnish with parsley and serve.