Heat oven. Preheat the oven to 425°F. Grease an 8-inch square cake pan with gluten-free cooking spray.
Whisk together cornmeal, gluten-free flour, sugar, baking powder, and salt in a large bowl. Add the milk, eggs, and oil. Whisk until combined. Batter will be thick. If it's too thick to spread, add two tablespoons of additional milk.
Spread batter into pan. Bake until golden brown, about 20 minutes. A cake tester inserted into the center of the cornbread should come out clean. Let the cornbread cool, about an hour or overnight.
Preheat oven to 350℉. Cut the cooled cornbread into cubes, about 1-inch. Spread cubes onto a large ungreased baking sheet. Gently turn cubes and toast until cubes are golden-brown and aromatic, about 20 minutes. Halfway through, turn the cubes so they toast evenly on all sides.
Preheat oven to 350℉. Grease a 9x13-inch baking dish. Set aside.
Combine the cooled, toasted cornbread and cooked vegetables in a large mixing bowl. If using sausage and/or dried fruit, add them now. Gently stir everything together.
*Cornbread Notes
*Stuffing Notes