Put the spinach and watercress leaves on a dry heated frying pan, close the lid and hold over medium heat for 2-3 minutes. Remove the leaves, squeeze out excess liquid and chop. Cut the fish fillet into large cubes. Mix fish with chopped herbs, yogurt and cream, season with pepper. Divide the dough in half, roll it out and cut into equal rectangles of about 5x10 cm. Put the filling in the center of half of the rectangles, sprinkle with chopped dill, cover with the remaining dough rectangles on top, pinch the edges so that the filling remains in the center. Trim the edges with a sharp knife to make fish-shaped pies. Grease a baking sheet and pies with oil, sprinkle with sesame seeds and bake in an oven preheated to 180ºС for 10 minutes, until golden brown. Serve immediately.