Boil the potatoes until tender in salted water, then drain and mash them.
Heat some oil in a frying pan, then reduce the heat.
Lay a brik sheet flat, place a circle of mashed potato in the center.
Crack an egg into the center of the mashed potatoes.
Season with salt and pepper.
Add the filling: a bit of tuna, chopped parsley, chopped onion, capers, harissa, and grated cheese.
Fold into a triangle, sealing the edges tightly.
Fry in hot oil until both sides are golden and crispy.
Drain on paper towels, and serve immediately.