Defrost the puff pastry according to the package instructions
Preheat the oven to 350℉.
In a saute pan warm the olive oil and add chopped onion, garlic, salt and mushroom. Saute until soft.
Add the shredded chicken, cumin, black pepper and heat through. Make sure the mixture is not too wet or dry either. Take it off the heat add the cilantro, cheese and mustard, mix well and set aside.
Roll out the puff pastry and cut into 4*4 inch squares.
Working with one prepared square at a time place 2 heaping tablespoons of filling onto one side of the square.
Dip a pastry brush with egg wash (1 beaten egg plus 1 tablespoon water) and brush on the inside ¼ inch edge of the filled dough. Fold the dough in half. Using the tines of a fork, firmly press the edges together to seal. Repeat this process with remaining dough and filling and arrange on a parchment lined baking sheet.
Brush each empanada with egg wash. Bake for 35-40 minutes or until golden brown.
Serve hot or warm as is or with some chimmichuri. Enjoy!!!