In a large bowl, dissolve yeast in water and let stand until it bubbles, about 10 minutes. Slowly stir in whole wheat flour, scallions, rosemary, thyme, and sage. Mix well, cover, and set aside to rise in a warm place for about 45 minutes.
Stir in olive oil, salt, and 1.5 cups white flour to form a stiff dough. Turn out onto a lightly floured surface and knead for 10 minutes, adding more flour as necessary to keep from sticking. Shape into a ball, place in a large, lightly-sprayed bowl, and turn oiled side up. Cover with plastic wrap and set aside to rise until doubled in size, about 1 hour.
Preheat grill to medium-hot. Divide dough into six balls. On a lightly floured surface, roll balls into 18 cm circles (about 1 cm thick.) Gently place breads on grill and cook 2 to 3 minutes on each side, turning occasionally, until well marked and browned.
Makes 6 breads.