Put chicken breasts in the bottom of the slow cooker/crock pot. Then, toss in carrots, onion, and celery. Then, pour in the flour, the the chicken stock, and a little salt and pepper. Cook for 5 to 6 hours on low. Shred the chicken {I just used two forks and shredded it up while it was still in the crockpot} and then, add the half and half and frozen peas in about 15 minutes before serving.