Combine vegetable broth, chicken breasts, onions, oyster sauce, coconut sugar, salt, pepper, cloves, ginger, and star anise in a slow cooker.

Cook on High until chicken breasts can be easily flaked with a fork, about 1 1/2 hour. Stir in bean sprouts and bok choy. Continue cooking soup until bean sprouts are tender, about 1 hour.

Cut zucchini into thin noodles using a spiralizer.

Divide soup among 6 serving bowls. Top with zucchini noodles.