Thaw the pre-cooked and shredded chicken, or grilled chicken. If need be, saute 2 chicken breasts in oil until cooked through, then slice.
In a large skillet, heat the oil and then toss in the sliced peppers and onion. Saute for 4 to 6 minutes, or until onions begin to turn opaque. Add in the chicken with the taco seasoning and saute together for a few minutes. Remove from heat.
To serve, place tortilla chips on the plate or bowl, top with the chicken-pepper mixture, then add a pinchful of shredded cheese.
Serve Chicken Fajita Nachos with sides of guacamole, or salsa, or sour cream with side of fresh fruit or veggies.