Preheat the oven to 400 degrees F. Grease a 9X13 inch baking pan.
Combine the cornmeal and milk in a medium bowl and let it stand for at least 10 minutes.Combine the flour, baking powder, salt, and sugar in a large mixing bowl. Using an electric mixer, beat in the eggs and oil just until the mixture is crumbly. Add the milk/cornmeal mixture and beat just until combined, about 30 seconds. Be careful not to over-beat or the cornbread will not rise properly. Stir in the quinoa, breaking up any lumps.
Pour the batter into the prepared pan and bake for about 35 minutes or until a toothpick inserted into the center comes out clean. Let sit for at least 5 minutes before cutting. Serve immediately while warm.