Dice the onion. Place the diced onions and chicken into the crockpot.
Pour the soup, chicken broth, poultry seasoning, salt and pepper into the crockpot. Gently stir it all around.
Cover and set the slow cooker to LOW. Cook for 4 hours, until chicken is tender.
Remove the chicken from the crockpot. Shred with forks. Place the chicken back into the crockpot. Add the bag of frozen vegetables.
Cut the biscuits into quarters. Arrange the biscuits in a single layer in the crockpot. Cover and set the slow cooker to HIGH. After 1 hour, gently spoon the chicken mixture over the biscuits so that they are covered. Cook 90 minutes more, until biscuits are no longer raw inside.