Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking dish.
Place the cornbread cubes into a large bowl. Set aside until needed.
Place the chicken breasts in a pot and cover with water. Add salt to taste. Bring to a boil, and cook until the chicken is no longer pink and juices run clear. Remove the chicken breasts from the pan, reserving at least 2 cups of the chicken broth. When cool enough to handle, remove the skin and debone, discarding the skin and bones.
Mix the onion, chicken broth, and red pepper with the cornbread; mash the mixture using a hand masher. Season to taste with sage, salt, and black pepper, adding a little at a time. Stir in the chicken. Spoon the mixture into the prepared baking dish.
Bake in preheated oven until top is golden brown, about 45 minutes.
