To roast poblanos, slice in half, seed, flatten halves with palm of hand and place skin-side-up on cookie sheet. Broil for about 10 minutes on top rack of oven until skin is brown and bubbly. Immediately remove to plastic bag or container and place in refrigerator (this makes peeling skin very easy later!).
Meanwhile, season chicken with garlic salt and black pepper. Bake at 425° for about 30 minutes.
Remove chicken from oven and set oven temp at 350°. Allow to rest to maintain juiciness. Reserve cooking juices. Shred chicken by lightly pulsing in blender or pulling apart with two forks. Set aside.
Peel and discard skin from cooled poblanos. Place poblano "meat" in blender, add cream of chicken soup and reserved juice from chicken's baking pan. Puree until smooth.
Place about 2 Tbsp shredded chicken in a tortilla and top with a little shredded cheese and onion. Roll up and place in 11x13 baking dish. Repeat for all tortillas in package.
Sprinkle tops of enchiladas with any extra cheese and onion. Pour poblano cream sauce over enchiladas, covering completely. Bake in 350° oven for about 30 minutes, til warmed through. Serve with side of rice and shredded lettuce.