Preheat your oven to 420 degrees.
Grease a baking tray with oil and fix parchment paper in it.
Chop the chicken finely (use a food processor). Afterward, transfer it into a bowl.
Saute the sun-dried tomatoes, spinach, mushrooms, minced onion, and tomato paste in melted butter for about two minutes or until the mixture gets fragrant.
Add the chicken stock and boil it until the spinach starts to shrink. Stir in the chicken until it is fully incorporated.
Cook on low for 3 to 4 minutes so the flavors may sink into the chicken.
You can cut the puff pastry sheets into any shape you like. Triangles are what I created.
Evenly distribute 1 spoonful of the chicken mixture over the pastry.
Add a tiny bit of mozzarella after that.
Fold the pastry dough over the filling and press it down using a fork on the sides.
After coating the pastries with the egg wash, lay them approximately 1 inch apart on the baking sheet that was already prepared. In around ten minutes, bake until golden.