Prepare the poaching liquid: Combine water, salt, cilantro, garlic, onion, bay leaf and peppercorns in a skillet with a lid, bring to a simmer and simmer for 10 - 15 minutes, or until the water is very well seasoned. Add the chicken and simmer over low heat, just barely a bubble, for 5 minutes, turn off the heat, cover and let sit for 10 minutes. Remove the chicken, set aside to cool. Discard the poaching liquid. Once the chicken is cool enough to handle, shred it using your fingers or two forks. Set-aside.
While the chicken cools, heat the oil in a medium skillet over medium-low heat, add the onion and cook, stirring, until soft, about 5 minutes, add the seasonings, and stir in well, then add the tomato, green chili, and chicken stock, mix well. Add the shredded chicken, mix well, then allow to simmer 5 minutes or so. Turn off the heat and allow to cool slightly.
As the chicken and sauce cool slightly, heat the oven to 350°F. Spray the tortillas on both sides with cooking spray, or lightly coat with oil, place, in a single a layer as possible, some overlap is ok, on a cookie sheet and place in the oven for about 3 minutes, or until soft and pliable. Remove from oven and stack to maintain softness and heat. Increase oven to 375°F.
Combine the cheddar and jack cheese together. Mix the two enchilada sauces together. Put about ½ cup of the sauce in the bottom of a baking dish just large enough to hold the enchiladas, about 12" X 9". Fill each tortilla with about 2 heaping tablespoons of filling, placing the filling in the center, add a small amount of chopped black olive, if using along with a pinch of the cheese mixture. Take one end of the tortilla and fold it over the meat/cheese mixture, pull back slightly to encase the filling, then roll the tortilla and place, seam side down into the prepared pan. Continue until all the tortillas have been filled, placing each new enchilada closely next to the others. When done, spoon the rest of the enchilada sauce over, making sure to cover all the tortilla, then sprinkle the remaining cheese mixture over, along with the cotia cheese, if using. Spray a piece of aluminum foil with cooking spray, then cover the casserole. Place in the oven and cook for 15 minutes, remove the foil and cook for 10 - 15 minutes more, or until the cheese is melted and the sauce is bubbling. Remove from oven, allow to sit for 5 minutes, then serve on warmed plates.