Wash lemon with hot water and rub dry. Finely grate the peel with a rasp. Peel and wash the potatoes and cut them into approx. 1 cm thick strips. Heat lard in a large pan.
Fry the potatoes over medium heat for 20-30 minutes, turning. Season with salt. Meanwhile wash the asparagus, cut off the woody ends and slice the asparagus diagonally. Cut fish into strips with a sharp knife.
After 10 minutes add the fish and asparagus to the potatoes. Turn carefully with a spatula. Whisk eggs and lemon zest. Season with salt and pepper. Pour egg mixture into the pan shortly before the end of cooking time.
Allow to set while stirring. Serve in the pan with lemon wedges.