Cut avacado in half, remove pit and scoop flesh into a small mixing bowl. Using a fork, mash the avocado until nearly smooth. Squeeze lemon or lime juice into bowl and mix to combine. Sprinkle salt, pepper and garlic powder (to taste)into avocado and mix completely. Stir in chicken, tomatoes, onion and bell pepper until everything is evenly coated. Scoop mixture into clean, dry tomaine leaves and enjoy!