Knead the flour with the yogurt, melted margarine, and yeast for 3 minutes. Leave to stand for 15 minutes. Soak the trachanas for 20 minutes in two cups of water, and then add the sugar and cinnamon and stir. Butter a medium-sized baking tin, take half of the pastry dough and spread it out by hand till it covers the bottom of the tin, reaching the sides. Add the trachanas, and then cover with the remaining pastry. Bake in a pre-heated oven at 200^oC for 40 minutes.