In the bottom of a large glass bowl, place cornbread cubes. Layer beans, corn, onion, bell pepper, tomatoes and 2 cups cheese on top of cornbread. Spread ranch dressing evenly over cheese. Cover, and refrigerate for at least 2 hours. Garnish with fresh parsley, if desired.
Preheat oven to 375°.
Generously season a cast iron skillet with up to 1/4 cup vegetable oil. Preheat the pan either in the oven or on the stove over medium-high heat.
Mix 1/2 cup oil, cornmeal, flour, cream-style corn, eggs, sour cream and cheese (if desired) in a large bowl, stirring with a wooden spoon or rubber spatula until combined. Pour batter into the preheated cast iron skillet. Place skillet in the oven and bake until golden brown, approximately 30 minutes. If making individual size cornbreads in smaller pans, they will require a shorter cooking time.