Make the filling: Place the potatoes in a pot of water and boil until fork-tender (20 minutes). Drain. Meanwhile, saute the onions in the oil until softened. Mash the potatoes and stir in the onion mixture and spinach.
Make the dough: In a mixer fitted with the paddle, combine the oil, water, cumin, turmeric, salt and 1 1/2 cups flour. If necessary, add additional flour or water to make a soft dough. Form into two balls. Wrap in plastic and let rest, at room temperature for 30 minutes.
Assembly: Roll the dough out into 2 rectangles, 1/8-inch thick (approximately 15 by 10-inches). Lay filling down center in a squared off log. Place the salmon in a layer on top of the filling. Trim dough and roll up. Refrigerate for 20 minutes.
Preheat the oven to 375 degrees F.
Slice into 2-inch pieces. Set, seam side down, on a non-stick cookie sheet or a sheet lined with parchment paper. Bake for 30 minutes, until golden. Garnish platter with flat-leaf parsley.