In a large mixing bowl, combine the softened cream cheese, grated Parmesan cheese, mayonnaise, garlic powder, onion powder, and pepper. Mix well until the ingredients form a smooth and creamy filling. Fold in the thoroughly dried spinach.

Sprinkle flour on a clean counter and unroll your puff pastry sheet. Spread the spinach dip filling evenly across the pastry, leaving one long edge clear to seal the pinwheel later.

Starting from the filled side, tightly roll the puff pastry toward the naked edge to form a log shape. Wrap the log in plastic wrap and refrigerate for at least 30 minutes.

Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

After chilling, unwrap the log and slice it into half-inch rounds. Place the pinwheels on the prepared baking sheet, ensuring they are spaced apart. Brush with a beaten egg mixed with a splash of water.

Transfer to the oven and bake for 15-20 minutes, or until the pinwheels are puffed and golden brown. Let cool for a few minutes before serving.