In a medium bowl, whisk together dry ingredients, flour through sugar. Add the seeds and scallions and stir to coat.
Make a well in the center, then pour in the buttermilk. Using a rubber spatula or wooden spoon, stir until you have a shaggy dough. Turn the dough onto a lightly-oiled surface (like a plastic cutting board) and gently knead it into a cohesive ball. Return ball of dough to bowl and cover with plastic wrap or a kitchen towel for 30 minutes. Heat the oven to 300° F.
Turn dough out onto a lightly floured surface and divide into four. With a floured pin, roll one ball out to ⅛- to ¼-inch thick, about 6 inches long and 4 inches wide.
In a large, heavy skillet (preferably cast-iron), heat 1 tablespoon olive oil over medium-high. When the oil is very hot, add the flatbread. Cook until deeply charred, about 3 minutes, then flip and continue to cook, 2 to 3 minutes more. Transfer to a baking sheet, sprinkle with flaky salt, and keep warm in the oven while you repeat the process with the remaining three pieces of dough and remaining olive oil.
Enjoy warm, or wrap in aluminum foil, store at room temperature, and reheat in the oven the next day.