1. Preheat oven to 425°F.
2. Combine soymilk and vinegar and let stand.
3. Mix dry ingredients in a large bowl.
4. Add the soymilk mixture and the oil, and stir until just blended.
5. Spread the batter into a nonstick or lightly oil-sprayed 9-inch square baking dish, and bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.
6. Serve hot.