Prepare all ingredients. Wash the onion and peel it. Boil two eggs hard and peel.
Prepare the dough for the pie: pour room temperature kefir into a deep container, add two raw eggs, vegetable oil, a pinch of salt and mix everything well. Sift the flour with baking powder and pour into a container with kefir. Mix everything with a whisk until you get a homogeneous dough without lumps.
Prepare the pie filling. To do this, cut the boiled eggs into small cubes and finely chop the onion. Drain all the oil from the canned tuna and add to the eggs and onions. Mix the filling well and add salt and pepper to taste.
Grease a baking dish with oil and pour in half the dough. Spread all the tuna filling evenly onto the dough. Pour the remaining dough over the filling and sprinkle with sesame seeds. Bake the pie in an oven preheated to 180℃ for 40-50 minutes.
Serve the tuna pie in portions, adding a sprig of herbs, a few slices of fresh tomato and cucumber.