Place chicken breasts into a large pan over medium heat and allow them to cook fully.
While chicken cooks slice onion and all peppers. Place these all in another pan along with some coconut oil and sautee them.
When chicken is finished remove it from the hear and with two forks shred the chicken to your liking. Place the chicken back into the pan along with the water and taco seasoning (http://paleowod.wordpress.com/2011/02/13/paleo-taco-seasoning/) and mix it all together well. Heat all ingredients and allow the chicken to simmer in the seasoning and water for 20 minutes.
Place chicken, onions, peppers, sliced avacado, and all your other favorite taco toppings into the romaine lettuce shells and enjoy!