Shred or chop cooked chicken (I like to use a rotisserie chicken) until you have about three cups of chicken.
In a medium skillet, add olive oil, onion, and chicken. Cook until onions soften, 3-4 minutes. Then add seasonings and remove from heat.
Heat fry oil in a high-walled skillet over medium heat. Working with one flour tortilla at a time, fill with a about 1/4 cup of filling and a small handful of grated cheese. Roll the tortilla into a tight cylinder. Place the rolled flauta in the hot oil, seam-side down so it seels.
Continue to roll the flautas as you fry the flautas until you run out of filling. Fry the flautas for about 2 minutes per side until they are golden brown.
Remove flautas from the hot oil and let drain on a few paper towels.
Serve flautas with avocado, cilantro, sour cream, and salsa.
Leftover flautas keep great in the fridge for a few days. Reheat in a 300˚F oven for a few minutes until warmed through and crispy.