Preheat the oven to 375°F (190°C) and lightly spray an 8x11-inch baking dish with nonstick spray.
Pound each chicken breast to an even 1-inch thickness using a meat mallet or rolling pin, then season both sides with salt and black pepper.
Place the seasoned chicken breasts in the prepared baking dish in a single layer.
In a medium bowl, whisk together the enchilada sauce, drained diced tomatoes with green chilies, and sour cream until smooth.
Pour the sauce mixture evenly over the chicken breasts, coating them well.
Bake uncovered at 375°F for 20–30 minutes, until the chicken reaches an internal temperature of 155°F–165°F (the residual heat will finish cooking while resting).
Sprinkle the shredded Mexican cheese blend evenly over the chicken and return to the oven just until the cheese melts and begins to bubble, about 2–4 minutes.
Remove the dish from the oven and let the chicken rest for 3–4 minutes.
To serve, arrange a nest of tortilla chips on plates, place a chicken breast on top, spoon any extra sauce over the chicken, and garnish with chopped cilantro and crumbled Cotija cheese.
