Preheat the oven to 425°F. Line a large rimmed baking sheet with parchment paper.
Divide the pizza dough into two equal portions. On a lightly floured work surface, using your fingers, press out each piece of dough to a roughly 4 x 8-inch rectangle. Using a pizza cutter or sharp knife, cut each rectangle into 12 equal-size squares or rectangles.
Cut the mozzarella into 24 (1-inch) cubes. You will only need about three-quarters of the block of cheese. Save the rest for another use.
Place one cheese cube in the center of each square of dough. Pull the edges of dough up and around the cheese, and press to seal, making 24 cheese-stuffed balls. Arrange the balls, seam-side down, in a Christmas tree shape on the prepared baking sheet, gently smooshing them together so they are all touching.
In a ramekin, whisk together the egg with 1 tablespoon of water. Brush the assembled dough-ball tree with the egg wash. Bake for 15 to 20 minutes or until golden.
While the tree bakes, melt the butter in a small saucepan over medium heat. Stir in the garlic powder, a pinch of salt, and parsley. Remove the pan from the heat and set aside.
Pulse the Parmesan cheese in a food processor until it is very finely ground.
When the tree is done baking, remove it from the oven and transfer it to a serving platter. Brush it with the butter-herb mixture, then dust the top with the Parmesan cheese. Serve warm or at room temperature with marinara sauce for dipping.