Fill a medium size saucepan halfway with water. Add salt and place on high heat.
While waiting for water to boil, peel onion and garlic. Cut the onion into four large pieces and set ¼ aside.
Carefully add roma tomatoes, ¾ of your onion and garlic cloves to the water and cover. Boil for 8-10 minutes.
While veggies boil, slice up remaining onion. Saute in olive oil on medium heat until they begin to caramelize.
Transfer boiled tomatoes, garlic and onion to a blender. Add chipotle peppers in adobo (add only half of the can if you don't want the sauce to be too spicy), Mexican oregano, ground cumin, juice from one lime and a pinch of salt. Puree until smooth.
Taste test your sauce, add more salt if desired.
Pour about half of your tinga sauce into the frying pan with sautéed onion. Stir in shredded chicken and chopped cilantro.
Preheat oven to 350°F. Spread a bit of sauce into the bottom of a 9x13 baking dish.
Soften tortillas by wrapping them in a damp paper towel and microwaving for 30-60 seconds (you can also soften them by frying in a little oil, this is very tasty but does add quite a few calories, so I tend to stick to the microwave option).
Portion chicken tinga filling and shredded cheese into softened corn tortillas, roll and line in the dish.
Cover enchiladas with sauce and cheese and bake for 20-25 minutes. (Tip: to avoid soggy enchiladas, don't completely drench them in sauce. Leftover sauce can be used as a topping)!
Once enchiladas are done baking, allow them to cool a bit. Serve with desired toppings and enjoy!