Whisk together flours, salt and baking powder in a mixing bowl. Add 3 tablespoons oil, buttermilk, and water and blend until smooth. Mix in scallions.
Cover the bowl loosely with a towel, plate or plastic wrap. Let rest for 30-40 minutes.
Preheat oven to 400 degrees. Grease a large baking sheet with the remaining oil. Scoop dough onto baking sheet and spread out evenly to the pan edges with a rubber spatula that has been moistened with water.
Bake for about 15 minutes until barely done, then change oven to low broil setting. Move pan to the upper oven rack and broil the top 1-2 minutes. Watch carefully so it doesn't burn. The pan may need to be rotated around for even browning.
Use a pizza cutter or sharp knife to cut into 16 rectangular pieces (4 rows x 4 rows)
Buttermilk substitution: Place 2 teaspoons vinegar or lemon juice into a measuring cup. Add milk until it reaches 3/4 cup. Let sit - 5 minutes until it thickens.