Preheat oven to 400F, grease a 9" x 13" pan or a pan size close to that.
Prepare leeks, cut them into bite-sized pieces, and rinse.
Mix eggs, yogurt, and oil in a bowl; add the cornflour into the egg mixture and whisk together; let sit for 3 minutes.
Sift together the flour, pepper, salt and bang powder with a whisk; add flour to the egg mixture and mix together with a wooden spoon or spatula.
Add the leeks and feta cheese; combine with the wooden spoon or your hands.
Or you can add the leeks and feta cheese to the egg mixture first, then add in the flour mixture.
Pour over in pan and press evenly across pan.
Bake for 25-30 minutes. Cut into squares. Enjoy warm.