In Yemen, where Shuli Madmone's parents were raised, this flatbread would be baked on the sides of an outdoor oven resembling an Indian tandoori.
Put the water in a medium bowl, and sprinkle the yeast over the water, stirring with a fork to dissolve. Let stand 10 minutes. Stir in half the flour, the flax seed and the salt, then stir in the remaining flour and mix well. The dough will be too sticky to knead. Scrape down the sides of the bowl. Cover the bowl with plastic wrap and let rise until doubled, about 1 1/2 hours, depending on how warm your kitchen is.
Stir it down, re-cover and let rise until doubled again, about 1 hour.
Preheat the oven to 550° or to its highest setting. Place a rack in the bottom of the oven and another rack in the top third. Line two rimmed baking sheets with parchment paper.
With oiled or moistened hands, take a clump of dough about the size of a tennis ball (one-sixth of the dough, weighing just under 6 ounces), and let it drop from your hands onto one of the lined baking sheets. Put 3 dough mounds on each sheet, spacing them evenly. Oil or moisten your hand again and flatten each mound until it's about 1/4-inch thick, roughly 7 to 8 inches long and 4 to 5 inches wide. The precise shape is not important. Scatternigella seeds over the surface, using about 1/2 teaspoon per bread. Press the seeds in place lightly with your fingertips.
Bake until the bread is browned and firm, about 12 minutes, shifting the position of the baking sheets halfway through. The bread should sound somewhat hollow when rapped with a spoon or your knuckles. Let breads cool on a rack for at least 15 minutes.
Flat bread makes a delicious accompaniment for dips, soups, or for spreading your favorite toppings.