Peel and slice the onions and avocado. Slice the tomatoes, cut the lettuce, and shred the cheese.
Slice the chicken breasts into thin strips. To achieve the best results, you should always slice chicken against the grain. This means that you want to look for the tiny lines in the chicken breasts, and cut across them rather than cutting in a line with them.
Heat up some vegetable oil in a pan on medium heat. Add the chicken breast strips and seasoning, and turn to coat the chicken evenly in the spices. Cook for a few minutes until golden, then flip and cook on the other side. The chicken only requires about 5 minutes of cooking in total, depending on how thick your chicken pieces are. Remove the chicken from the pan.
Add a flour or corn tortilla to the same pan that you just used to cook the chicken. Leave it for about 10 seconds, then flip. The tortilla will be warmed and softened, and also retains some flavor from the chicken seasoning. Repeat with the other tortilla(s).
Place the tortilla on a plate. Spread some mayo over the top. Then, add lettuce, sliced onions and tomatoes, avocado, and finally the chicken.
Wrap it up using your favorite method.