Peel, wash and dice the potatoes. Drain the beans, rinse with cold water and drain. Peel onions and dice them roughly. Heat oil in a large pan. Fry the potatoes for about 10 minutes. Turn several times in between. Season with salt.
Add onions and beans and fry briefly. Whisk eggs and milk. Season with salt, pepper and chilli powder. Pour on egg milk and let it falter at low heat. Close the pan with a lid. Wash parsley, dab dry and chop. Sprinkle over the tortilla
Tip: For smaller tortillas, divide cooked potato and bean vegetables into 2-4 portions and pour 1/2 or 1/4 of the egg milk on each and allow to set