A monk said to Joshu, "I have just entered this monastery. Please teach me." "Have you eaten your rice porridge?" asked Joshu. "Yes, I have," replied the monk. "Then you had better wash your bowl," said Joshu. With this the monk gained insight.
My interpretation differs from the one given by the translator. I think Joshu is saying that 'teaching' or 'learning' can occur in your everyday life, even when doing the most mundane activities if your focus is right and your mind is disciplined. I believe one of the goals of sitting in zazen and practicing Zen is to carry the mindset you reach during satori into your everyday existence. You are truly enlightened when that mindset is your constant state of existence.
In short, Joshu is saying: be in the moment and learning will come.