Pat chicken dry and season with salt and taco seasoning.
Add oil to a skillet over medium-high heat.
Once hot, add cubed chicken and press into an even layer and sear, 2-3 minutes per side, until cooked through (internal temperature 160° F)
Remove the chicken to a clean dish and set aside.
Add the onions and cook for about 5-7 minutes or until soft and translucent.
Add the chicken back to the skillet with the onions. Spoon in the salsa and toss and cook for about a minute to combine the ingredients.
Remove the chicken mixture and set aside. Wipe out the skillet with a paper towel.
Place a tortilla in the skillet and top with some shredded cheese and ⅓ of the chicken mixture. Top with more cheese and another tortilla.
Cook, 3-4 minutes per side until cheese melts and tortilla browns.
Repeat with the remaining tortillas, cheese, and chicken mixture until you have 3 quesadillas.
Serve with guacamole, salsa, or toppings of choice, and enjoy!