Boil potatoes with salt. Peel and mash. Combine with salt, white ground pepper, key lime juice, aji and oil.
Mix tuna fish with mayonnaise and diced onion.
Spread potato mixture on a thin rectangular sheet of plastic. Spread the filling: top with tomatoes, sliced avocado and roll using the plastic to help form a round loaf.
Refrigerate for one hour, remove plastic and place on a serving dish. Garnish with parsley, chopped olives and hard boiled eggs, sliced avocado (with drops of key lime juice to prevent discoloring) and if desired, mayonnaise and red pepper slices.
If canned tuna fish is used, season with key lime juice and chopped onion.
If fresh tuna fish is used, bake first with salt and ground white pepper.
Different fillings for Causa:
Avocado, mayonnaise, diced tomato and boiled diced eggs.
Avocado, mayonnaise, beets and boiled diced eggs.
Shrimps, mayonnaise, ketchup, drops of lime juice and ground yelow aji.
Crabmeat and mayonnaise.
Octopus in olive sauce.
Olives and mayonnaise.