Clean sliced leeks in large bowl of water — gritty soil often hides between the vegetable's layers. Dry the washed leeks well on a kitchen towel.
In large sauté pan, warm olive oil over medium heat. Add dry leeks, sliced potatoes, salt and pepper. Cook until vegetables are soft, gently tossing, about 10 minutes. Turn off heat and add in the chopped dill, crumbled feta and lemon juice. Allow filling to cool slightly as you roll out pastry dough.
Dust counter with flour and roll dough disk into a 14-inch-thick round. Don't worry about creating a perfect circle. Fill middle of pastry with vegetable mixture, leaving a 1-inch border of dough all the way around. Fold border of dough up around the filling and bake for 25 to 30 minutes, until crust is slightly golden.