Heat oven to 475° F.
To make dough: In mixing bowl, combine whole-wheat flour, 1/2 cup all-purpose flour, yeast and salt. Add water and oil. Beat until smooth. Stir in remaining all-purpose flour to form soft dough. Place onto floured surface and knead by hand until consistent and elastic, about 4 minutes. Cover and let stand 15 minutes.
To make topping: In bowl, combine mushrooms, tomatoes, green bell pepper, olives, onion, oil, vinegar, salt, pepper, oregano, thyme, basil and garlic powder.
Coat 15-by-10-by-1-inch baking pan with nonstick cooking spray. Sprinkle with cornmeal. Gently press dough into pan. With fork, generously prick dough.
Bake 10 minutes, or until lightly browned. Cover dough with topping mixture. Bake additional 10 minutes, or until edges are golden brown.