Preheat the oven to 400°F (200°C). Line a rimmed baking sheet with parchment paper.
Thaw the puff pastry according to package directions, then unroll or unfold each sheet on a lightly floured surface.
Cut each puff pastry sheet into 9 equal squares and arrange them on the prepared baking sheet, leaving a small gap between squares.
Spoon a thin layer of marinara sauce onto the center of each puff square, leaving a 1/4–1/2 inch border around the edges.
Top each sauced square with pieces of thawed popcorn chicken, then scatter mozzarella pearls over the chicken and sprinkle with grated Parmesan.
Season the tops lightly with garlic powder and Italian seasoning to taste.
Whisk the large egg with 1 tablespoon water to make an egg wash, then brush the exposed edges of each puff square with the egg wash.
Bake in the preheated oven for 15 to 18 minutes, or until the pastry is puffed and golden brown.
Remove from the oven and garnish with fresh basil before serving.
