In skillet, heat oil over medium heat; sauté shallots and garlic for 2 minutes or until tender. Add spinach, oregano, salt, pepper and hot pepper flakes; sauté for 3 minutes or until moisture has evaporated. Squeeze to remove any additional moisture. Shred chicken if in chunk form. Stir in chicken. Preheat oven to 400°F. Line baking sheet with parchment paper. Lightly whisk egg with 1 tbsp. water to make egg wash. Cut out 5 rounds of dough from each sheet of puff pastry using 4-inch cutter. Brush edges of each round with egg wash. Add 2 tbsp. chicken filling to center of each round; fold over to enclose filling. Seal edges with fork and brush tops with egg wash. Transfer to prepared baking sheet; bake for 20 to 25 minutes or until pastry is golden brown. Cool for 10 minutes. Serve with tzatziki for dipping.