Preheat oven to the warm setting (about 200°F) and line a baking sheet with foil.
Pour oil into a large saucepan or deep skillet to a depth of about 3/4 inch and heat over medium until the oil reaches 375°F.
In a medium mixing bowl, combine the shredded chicken, shredded Mexican blend cheese, salsa, diced chiles, garlic salt, and pepper. Stir until evenly mixed.
Working with a few tortillas at a time, place a heaping spoonful of the chicken mixture along the center of each 6-inch tortilla and roll tightly. Secure each roll with a toothpick.
Using tongs, hold each flauta in the hot oil until the tortilla firms up, then release it to continue frying. Fry until golden brown, about 2 minutes, turning as needed.
Remove fried flautas to a paper towel–lined plate and immediately season with salt. Transfer to the foil-lined baking sheet and keep warm in the oven while you cook the remaining flautas.
Serve the flautas warm topped with shredded lettuce, chopped tomatoes, green salsa, guacamole, and Cilantro Ranch dressing as desired.