In a medium bowl, mix the chicken, green enchilada sauce, onion and 1 cup of the cheddar cheese.
Pre-heat a 12-inch cast iron camp Dutch oven to 350 F degrees (25 coals total: 17 top/8 bottom, see note #1.)
Evenly split the chicken mixture on the tortillas and roll them up.
Spray the bottom and sides of your Dutch oven with cooking spray.
Pour 1/4 of the red enchilada sauce in the bottom of the Dutch oven.
Lay the rolled tortillas in the sauce in the oven with the seam side down.
Pour the remaining red enchilada sauce over the top of the enchiladas.
Cover the Dutch oven with its lid (and coals) and bake for 35-40 minutes until the enchiladas are heated through. Turn oven and lid 1/4 turn in opposite directions every 10-15 minutes for even baking.
Remove the cover and sprinkle the remaining 1 cup cheddar cheese over the enchiladas.
Replace the lid (with coals) and continue baking (about 5 minutes) until the cheese melts.
Remove the Dutch oven from the heat and remove the coals from the lid; let stand (covered but without coals) 5 minutes to firm the enchiladas.