Can you recount the story from Chapter 23 involving the Yogi, Nanasaheb Chandorkar, and the onions?

Certainly. Chapter 23 narrates an incident where a practitioner of Yoga, who was an expert in the Yoga Shastras but could not achieve Samadhi, came with Nanasaheb Chandorkar to see Sai Baba. He hoped Baba's grace would resolve his spiritual block. However, upon seeing Baba eating bread with onions, a strong doubt arose in his mind, making him question how such a person could help him. As Chapter 23 explains, Sai Maharaj, being omniscient, immediately perceived this doubt and remarked, "Nana, only those whose digestion is strong should eat onion." This profound statement startled the Yogi, instantly dispelling his doubt. He then surrendered to Baba with true devotion, listened to His teachings, and returned with a happy and peaceful mind.