Preheat oven to 350 degrees F. Grease 8x8-inch baking dish with cooking spray.
Combine dry ingredients in a large bowl including flour, cornmeal, sugar, baking powder, paprika, garlic powder, onion powder, cayenne, salt, and oregano.
Add creamed corn, canned corn, and green chilies, stirring until combined.
Whisk together buttermilk, yogurt, ½ cup melted butter, and eggs until well combined. Add wet ingredients with corn mixture, stirring until combined. Pour batter into prepared baking dish.
Combine crushed cornflakes with 3 tablespoons melted butter, tossing until cornflakes are well coated. Sprinkle cereal on corn casserole in an even layer. Bake casserole for 45-50 minutes or until deeply golden brown. The center should still be a little jiggly but the edges should be set.
Remove casserole from oven and serve warm or at room temperature.
Notes
You can also bake the casserole in a 9x9-inch baking dish. Adjust the baking time, checking the casserole at 35-40 minutes.