Prepare the toppings. Tear the lettuce, chop tomatoes, dice avocados, and clean and chop the cilantro. Set aside.
Slice onion and pepper fairly thin.
On a separate cutting board, cut the chicken into thin strips.
Fry the chicken in butter in a large skillet over medium-high heat. Salt and pepper to taste. When the chicken is almost cooked through, add onion, pepper, and Tex-Mex seasoning.
Lower the heat and continue to fry while stirring for a couple of minutes until the chicken is thoroughly cooked and the vegetables have softened just a bit.
Place lettuce in a bowl and add the chicken mixture. Add shredded cheese, diced avocado, chopped tomatoes, and fresh cilantro.
