Preheat the oven 375 degrees F. Combine the first 5 ingredients in a large bowl. Stir in the corn, cheese and green onions. Combine the buttermilk, 1/3 cup vegetable oil and eggs in a second bowl. Add the wet ingredients to the dry and mix until just combined. Set a 10 inch cast-iron skillet over medium heat. Add the 2 Tbsp. of oil and swirl to evenly coat the pan. Pour in the batter, and then place the skillet in the oven. Bake for 35 minutes, or until a toothpick inserted in the centre of the cornbread pulls out clean. Cool the cornbread on a baking rack for 5 minutes, and then invert onto a cutting board. Cut into wedges and serve.