In a small sized mixing bowl, add water (make sure it's warm, as hot water can kill the yeast), salt, yeast, ½ cup of flour, stir well and let it sit aside until the mixture gets bubbly.
In another medium sized mixing bowl add olive oil, salt, and 2 cups of flour, and mix together using a spoon.
Add the bubbly mixture to the rest of the ingredients, mix until it's all together enough to knead on a lightly floured work surface to knead.
knead for about 10 minutes then form a dough ball and let it sit in a bowl covered with a kitchen towel for about 1 hour or until the dough ball doubles in size (in a warm place to let the dough rise). When I don't have time to wait I place the bowl with the dough in another bowl that's filled with warm water (not hot!), the dough rises within 30-45 minutes.
To prepare the filling: (If using frozen spinach then defrost and thaw out the spinach but if using fresh spinach chop the spinach and then you have to squeeze out the juices a little) Saute a finely chopped onion with the spinach, add the lemon, sumac and salt, and let the juices dry out with the heat.
After the dough ball doubles in size, cut the dough in small balls (size of an egg) and keep under a towel so the dough does not dry out. Roll out each ball into a circle (I use my hands) then follow the pictures above to make the triangles.
Making sure that the triangles are sealed well, transfer on a baking sheet and brush the pastries with a beaten egg if not vegan, or with almond milk or tea if vegan (to achieve that beautiful golden color).
Bake on the middle rack at 200c for about 30 minutes or until the tops are golden.