Heat oil in frying pan over medium-high heat. Add chicken and cook until almost cooked. Add salt and pepper to taste.
Place chicken in a shallow baking dish and top each piece with 1 - 2 slices of tomato and 2 - 3 slices of cheese. Bake for 10 to 15 minutes or until cheese melts. Remove from oven, add 2 to 3 slices of avocado on top of each chicken piece and serve immediately.