You can cook the chicken any way you want, or even use rotisserie chicken, but for this batch I brined and baked it. To brine the chicken, add 1/4 cup Kosher or sea salt to a quart of water in a mixing bowl. Stir to dissolve the salt and add the chicken breast, letting it brine in the fridge for 30 minutes or so. If the chicken isn't fully submerged then add a bit more water. Once brined, pat dry the chicken breast and add it to a baking sheet.
Rinse and de-stem the tomatoes and tomatillos. Add them to the same baking sheet and bake everything at 400F for about 20 minutes or until the chicken is no longer pink inside (160F).
Once the chicken has cooled you can shred it with two forks and set aside until you need it.
Meanwhile, roughly chop a half onion and saute in some oil over medium heat. Add four whole peeled garlic cloves and saute until the onion is starting to brown.
Add the onion-garlic mixture to a blender along with 3 chipotles in adobo and the roasted tomatoes and tomatillos. I usually scrape out the seeds of the chipotles. Combine well and take a taste, adding more chipotles if you want more heat.
Add the Tinga mixture back to the same pan you used to cook the onion. Add 1 teaspoon Mexican oregano, a pinch of cumin (optional), 1/2 teaspoon of salt, freshly cracked black pepper, 1/2 cup stock (optional), and 1-2 tablespoons of adobo sauce (optional). Bring to a simmer and take a final taste for seasoning.
Keep 1/2 cup of the Tinga sauce in the pan and set the rest aside for later. Add the shredded chicken to the 1/2 cup of Tinga sauce and combine well.
If you are frying the tortillas, add enough oil to a skillet or saucepan to create 1/4" layer of oil. Bring it up to frying temp (approx. 360F and just over medium setting on my stove) and use tongs to give the tortillas about 5-10 seconds per side in the oil, or until they are just starting to crisp up. Set aside on some paper towels to drain. Always use caution when frying in hot oil -- I find it easiest to do them one at a time and use some longer tongs.
Add a single tortilla to a plate and fill with a couple tablespoons of the Chicken Tinga, plenty of cheese, a sprinkling of chopped onion, and any pickled goods you are using. Roll tight and place seam side down in a baking dish. Continue until you run out of chicken -- this single breast was enough for 8 enchiladas.
Bake for 8-10 minutes in a 400F oven or until the cheese is completely melted. Remove from oven and drench the enchiladas with the Tinga sauce.
Serve immediately and top with your choice of Crema, Cotija cheese or Queso Fresco, and freshly chopped cilantro.
Store leftovers in an airtight container in the fridge where they will keep for a few days.