Grate the zucchini, add salt, squeeze out excess water and strain in seive. Grate the cheeses, mix with the beaten eggs, zucchinis and chopped spearmint. Phyllo dough: In a large bowl, stir yoghurt with the oil or margarine and slowly add flour. Knead well and roll the dough into a ball. Cover with a linen towel and let it rest for about 30 minutes. Cut the dough in halves with one part slightly larger than the other. Roll out the phyllo and spread the larger crust on the bottom of a buttered or oiled baking pan, covering the sides of the pan. Pour the filling evenly on top. Cover with the remaining dough and roll the sides down like a pie. Brush with oil and top with sesame seeds.