Preheat oven to 425°. In a small bowl, beat 1 egg with 1 teaspoon water. Set aside.

In a large mixing bowl combine celery, carrots, onion, garlic, parsley, bread crumbs, Parmesan, salt and pepper. Mix well. Add remaining egg and turkey and mix until just combined. Do not overmix. With your hands, form 1 1/2" meatballs. In a large skillet over medium-high heat, drizzle olive oil and sauté meatballs until golden brown, 3 to 5 minutes.

In a 9" pie dish or baking dish spread 1 cup tomato sauce and arrange meatballs in an even layer. Top with remaining tomato sauce and mozzarella and arrange puff pastry pieces in a circular pattern. (Less overlap will help the puff pastry rise.) Brush lightly with egg wash and bake until pastry is golden brown, 18 to 20 minutes.

Garnish with parsley and serve immediately.