Preheat oven to 425°F. Add 2 teaspoons vegetable oil to a cast iron skillet, allowing it to preheat. Leave for 5 minutes to achieve thick, dark brown crust.
Combine cornmeal, flour, baking powder, salt, sugar, egg, mayonnaise, buttermilk, water, cheddar cheese, and drained pimentos in a bowl.
Remove the hot skillet from the oven and rotate it to coat the bottom. Pour the batter, being cautious, ensuring it sizzles. Sprinkle cheese and pimentos on top. Bake for 30 minutes or until golden brown.
Oven-defrost cornbread, invert, remove from skillet, preserve crisp crust, serve warm.