Place the onion, carrot, celery, bay leaves, and salt in the slowcooker. Top with the split or cut up chicken. Cover with the water. Cook on high for 4 hours.
Remove the chicken with tongs and let cool to the touch. This next step is optional but I like to do it for clearer broth. Remove and reserve the veggies with a slotted spoon. Pour the soup through a fine strainer or cheesecloth then return back to the slowcooker along with the veggies. Pull the meat from the bones and add it back to the soup, see my note above about saving the breast meat for another meal.
Season with more salt and pepper to taste. Place some zoodles in the bottom of a bowl and serve the hot soup over them.