1. Preheat oven to 425°. Sauté first 4 ingredients in hot oil in a 12-inch cast-iron skillet over medium heat 8 to 10 minutes or until tender. Remove from skillet; wipe skillet clean.
2. Stir together cornmeal mix, buttermilk, and next 4 ingredients just until moistened. Stir in onion mixture and chicken just until blended. Pour batter into hot 12-inch skillet.
3. Bake at 425° for 25 to 30 minutes or until golden brown.