Preheat oven to 200 C / Gas 6. Cover a baking tray with aluminium foil, spray with cooking spray and set aside.
In a frying pan, melt butter over medium heat. Cook and stir the chopped onion and spring onion until tender. Add chopped red pepper and cook for another 5 minutes. Crumble in the stock cube and mix well then season with salt, paprika and cayenne pepper. Add chicken in small cubes and stir well, letting it combine with the flavours in the pan. Remove from heat and let it cool down a little bit. Add chopped hard boiled eggs and olives, and mix well.
Place the empanada pastry discs on a flat surface. Wet edges lightly with warm water. Put 1 big dollop of filling in the centre, fold dough over, and seal edges by pressing with a fork. Transfer to the prepared baking tray.
Bake in the preheated oven for 10 to 15 minutes, until golden. Remove from the oven and let cool down for 5 minutes before serving.