• Preheat oven to 375°F. Spray a 9x13-inch baking pan with cooking spray. Set aside for now.

For the Chicken

• If using chicken breasts or thighs, place chicken in a large saucepan with onion, garlic, and salt. Cover with water and bring to a boil over medium-high heat. Reduce heat to medium-low and simmer until chicken is cooked through, approximately 15 minutes.
  2 pounds boneless, skinless chicken breasts, 1 onion, 4 cloves garlic, 1 tablespoon kosher salt
  
• Transfer chicken to a cutting board and let cool. Use two forks to shred the meat or cut the chicken into 1-inch cubes.
  
• If using rotisserie chicken, simply remove the meat from the skin and bones, and shred the meat or cut it into 1-inch cubes.

For the Green Sauce (Salsa Verde)

• Combine all the salsa verde ingredients in a blender or food processor and purée until smooth. Add a little water to smooth, if necessary.
  1 pound fresh tomatillos, 1 onion, 1 clove garlic, 2 serrano chiles, ½ cup chopped fresh cilantro
  
• Salt and pepper, to taste.
  Kosher salt and freshly ground black pepper

For Assembly

• First prepare the tortillas: In a medium sauté pan set over medium-high heat, heat the oil until it shimmers. Use tongs to place a tortilla in the hot oil. The oil should be hot enough for the tortilla to bubble immediately. Heat the tortilla for 10 seconds per side, or until it is lightly browned. Transfer the tortilla to a cooking rack placed over a baking sheet. Repeat with remaining tortillas. Work quickly.
  12 corn tortillas, ½ cup canola oil
  
• Place ½ cup green sauce (salsa verde) in the bottom of the prepared pan/dish and spread it around the dish.
  
• Place 2 tablespoons of chicken, 1 teaspoon of green sauce (salsa verde), and 1 tablespoon of shredded cheese into a tortilla. Roll it up and place it seam-side down in the dish. Repeat with the remaining tortillas, placing them right next to each other in the pan.
  2 cups shredded Mexican cheese blend
  
• Spoon green sauce over the top of the rolled enchiladas and sprinkle with half the crumbled cheese
  1 cup queso fresco
  
• Place the enchiladas in the oven and bake for 20-30 minutes, or until the middle enchiladas are heated through and the cheese is melted.
• Remove the enchiladas from the oven, but leave the heat on, and spoon green sauce over the enchiladas, down the length. Place them back in the oven for 5 minutes.
• Remove the enchiladas from the oven and drizzle with sour cream or Mexican crema. Sprinkle with the remaining crumbled queso fresco or cotija cheese, chopped tomatoes, chopped onion, and fresh cilantro. Serve immediately.
  1 cup sour cream, ½ sweet yellow onion, 2 fresh tomatoes, ¼ cup chopped fresh cilantro