Cut the fish fillet into large chunks, sprinkle with lemon juice, salt and fry in a deep frying pan with butter on both sides until golden brown. Remove the fillets and remove to a warm place. Peel and cut the potatoes circles. Fry until golden brown in the remaining oil with chopped onion, a little salt. Put the pan back into the fish, let the eggs on top, being careful not to damage the yolk, sprinkle with grated cheese and cook, covered over low heat until cooked fried eggs, sprinkle with fresh herbs.