Clean, wash and cut the spring onions into rings. Drain the beans in a sieve. Peel and wash the potatoes and cut them into fine slices. Heat oil in a coated pan.
Sauté the vegetables and potatoes while turning. Whisk eggs and milk. Season with salt and pepper and pour over the vegetables. Cover the vegetables and let them simmer at low heat for 15-20 minutes. In the meantime, peel and finely dice the onion and garlic for the sauce.
Fry in hot oil. Add the chopped tomatoes and let it boil down a little. Season the sauce with salt, cayenne pepper and chilli. Divide tortilla into 4 pieces, add sauce.