Remove any giblets from chicken then rinse chicken with water, inside and out, then pat dry with paper towels.
Rub inside and out the chicken with salt, pepper, and bouillon powder. Generously rub the chicken with homemade Creole seasoning, stuff it with 3 garlic cloves and lemon, then refrigerate until ready to cook. If time permits, do it the night before (up to 24 hours is best).
Remove chicken from the fridge when ready to cook, add sliced onions in the bottom of the slow cookers insert 4 smashed garlic cloves.
When ready to cook, add chopped onion, remaining garlic, and bay leaf to the bottom of a crock pot.
Place chicken over onions in the slow cooker, breast side up.
Tuck the potatoes, celery stalks, and carrots (optional) into available spaces all around the chicken. Add the thyme sprig.
Cover and cook chicken: Set the slow cooker to HIGH, and cook for 2½ to 3½ hours, or set it to LOW and cook for 4-5 hours. The exact cooking time will depend on the size and type of your chicken.
Chicken is well done when the internal temperature registers 165°F in the breast or 175°F-180°F in the thickest part of the thigh.
If desired, set the oven to broil, then carefully transfer the chicken from the slow cooker and place it in a roasting pan.
Broil for 5-8 minutes, until the skin is crispy and brown.
Remove from oven; let chicken stand 10 minutes before carving so the juices settle back into the meat.
Discard bay leaves, smashed garlic, and lemon.