Sift 2 cups flour, salt and baking powder together into a large bowl. Add scallions and stir to blend. Make a well in the center; add water, 2 tablespoons canola oil and sesame oil. Work the flour in toward the center with a spoon to incorporate the dry and wet ingredients. Turn the soft dough out onto a floured work surface and knead, using some or all of the remaining 1 cup flour, until smooth and elastic, about 5 minutes. Wrap in plastic and let rest for 30 minutes at room temperature.
Cut the dough into 12 equal pieces. Form into balls, then flatten and roll out into 8-inch circles.
Heat a large skillet over medium heat. Lightly brush the pan with canola oil and cook the flat breads until just golden, 1 to 2 minutes per side. (When the breads begin to form bubbles here and there, it's time to flip.) Serve hot.