For the pie crust, - mix the flour and the salt - add the butter - mix with your fingers for about 3min, so that the flour becomes granular - add water and keep mixing with your fingers until the dough is homogenous - put the dough in the fridge for at least 15min (thus the dough will be easier to spread)
For the filling, - cook the tuna (cut in small pieces) - cook the leek (with butter) - mix the eggs and the cream - prepare the dough in a pan, make small holes in the dough with a fork - put the cooked tuna and leek on the dough - add in lemon zest and lemon juice squeezed from the lemon - cover them with the mixture of cream and eggs - add grated cheese on the top
Put it in the oven about 25min 220°C