Place the Doritos in a large zip-top bag and crush them with a rolling pin until you have fine, even crumbs. You want a texture similar to panko breadcrumbs with a few slightly larger pieces for extra crunch. Pour the crumbs onto a wide plate or shallow dish.
Set up a breading station with three dishes. On the first plate, combine the flour, garlic powder, smoked paprika, and black pepper. In a shallow bowl, whisk together the eggs and milk until smooth.
Pat the chicken tenderloins dry with paper towels. Dredge each piece in the seasoned flour, shaking off excess. Dip into the egg wash, letting any extra drip off. Finally, press the chicken firmly into the crushed Doritos, turning and pressing to coat all sides evenly.
Preheat the air fryer to 380 degrees F. Arrange breaded chicken in a single layer in the basket, leaving a little space between pieces. Spray the tops generously with cooking spray.
Air fry for 6 minutes, then carefully flip each piece and spray the other side with cooking spray. Cook for another 5 to 6 minutes until the crust is deeply golden and the chicken registers 165 degrees F internally.
While the chicken cooks, stir together the sour cream, ranch seasoning mix, lime juice, and chopped cilantro in a small bowl. Serve the hot, crunchy chicken immediately with the dipping sauce on the side.