Preheat oven to 200 C / Gas 6. Cover 2 baking trays with aluminium foil and spray with cooking spray.
In a medium frying pan, melt 1 large tablespoon of butter. Cook and stir the chopped spring onions and garlic until tender, around 5 minutes. Add the chicken and cook and stir until no longer pink in the centre. Season with salt and pepper to taste. Remove from heat and let it cool down a little bit.
In the meantime place the empanada pastry discs on a flat surface and lightly wet edges with warm water. Put a large tablespoon of filling in the centre of each then fold pastry over and seal the edges by pressing with a fork. Transfer empanadas to baking trays and brush with egg.
Bake in the oven for 10 to 15 minutes, until golden. Remove from the oven and let cool for 5 minutes before serving.