In a large bowl, mix the chicken, garlic, onion powder and salt and pepper. Form chicken mixture into patties.
In a large skillet over medium heat, add the burgers and cook for 4 minutes on each side, until burgers are cooked through. Remove burgers from skillet and set aside half for lunch the next day (Burgers with Citrus Veggie Stir Fry).
In the same skillet, heat the ghee over medium heat. To the ghee, add the onion, lime juice, oregano and salt and pepper. Sauté for 5 to 10 minutes, until onions are caramelized.
In the lettuce leaves, layer the burger, onion, tomatoes, avocado and serve.