If you thought shrimp alfredo couldn't get any creamier, guess what? I'll let you finish that thought.
Preheat oven to 400°F. Heat 2 tablespoons of the butter in a large skillet over medium. Add shrimp and 1 1/2 tablespoons of the garlic; cook, stirring often, until opaque, 3 to 4 minutes. Transfer to a cutting board, and coarsely chop. Stir together shrimp mixture, alfredo sauce, peas, ham, cheese, salt, and pepper in a large bowl.
Spray an 8-inch square baking dish with cooking spray. Spoon shrimp mixture into prepared baking dish. Roll pastry sheet to a 9-inch square, and top dish with puff pastry sheet. Cut 4 slits in center of pastry.
Place remaining 1 tablespoon butter and remaining 1 1/2 teaspoons garlic in a small microwavable bowl, and microwave on HIGH until melted, about 45 seconds. Brush over puff pastry. Bake in preheated oven until pastry is lightly browned, about 20 minutes. Reduce oven temperature to 350°F. Continue baking until golden and puffed, about 15 more minutes. Let stand 10 minutes before slicing. Sprinkle with parsley.