Start by making the pastry. Sift the flour with the salt and baking powder. Mix in about 6 tablespoons water, a little at a time, until the dough is gooey, but not wet. Add 1 tablespoon olive oil, plus another teaspoonful, and a little more flour, if needed, to make a cohesive mass.
Knead the dough for 5 to 10 minutes, until smooth and elastic. Cover it and set aside to relax for an hour or two.
For the filling, separate the curly endive leaves, so the vegetable will cook in the same time. Steam the spinach and endive together in a large pan, in the water clinging to the leaves, plus just an extra 1/2 cup. Turn the leaves over occasionally, so they wilt evenly.
When they are wilted, but not mushy, drain them in a colander, pressing firmly with the back of a wooden spoon to remove as much excess liquid as possible. (Reserve the liquid for use in soup, or drink with a squeeze of lemon juice, as the Greeks do.)
Saute the scallions in 2 tablespoons olive oil, until barely soft. Add a few tablespoons of water if they stick to the pan. Roughly chop the cooked spinach and curly endive and finely grate the zest from the lemon. Then toss the cooked vegetables with the scallions, parsley, dill, lemon zest and 1 tablespoon lemon juice, salt, and pepper, adding 3 tablespoons olive oil. Set aside until you are ready to fill the pastry.
Choose an ovenproof earthenware or glass baking dish 2 to 2-1/2 inches deep and about 2-quart capacity and brush the inside with oil. Divide the pastry into two unequal parts, and then again into halves. On a floured surface roll out one of the larger pieces of pastry. This should be large enough to line the dish, coming up and over the sides - this should make it very thin. Fit it into the baking dish and brush it with olive oil. Do the same with the second piece of pastry, placing it on top of the first, and brush again with olive oil.
Sprinkle the tablespoon of rice or cracked wheat over the bottom, to soak up excess juices, and fill with the spinach and herb mixture. Roll out the remaining two pieces of pastry, separately, to fit the top of the dish. Place the first on top of the spinach, brush with olive oil, then place the second on top of that. Prick the pastry with a fork in an attractive pattern and brush the entire top with olive oil. Sprinkle with sesame seeds. Bake in an oven preheated to 350 F for 45-50 minutes, until golden brown.