Preheat the oven to 180 degrees Celsius (350 degrees Fahrenheit).
Grease 1 biscuit sheet.
Place the biscuit mix, orange zest and oil in a bowl and mix, then add the tablespoons of water one by one and knead until a firm and elastic texture is achieved (plasticine consistency, it should not stick to your hands).
Add the prune pieces and mix well.
Form small balls of dough (of similar size), arrange them on the baking sheet and flatten them 1 by 1 (leaving enough space so that they don't stick together when baking).
Bake for 15 to 20 minutes or until golden brown, remove the tray from the oven and leave to stand for 10 minutes on a wire rack.
Remove the biscuits and place them directly on a wire rack and let them cool completely.
You can store them in an airtight jar, but use them as soon as possible.