Onion smell getting on fruits
My experience is that washing doesn't effectively get rid of onion or garlic odors from cutting boards. 

Either get another - maybe lighter weight and cheaper - cutting board for fruits, or flip your current board over, and use the "bottom" side for delicately scented items, etc. Mark the "top" side with an "o" for "onion" (or some such discreet indicator) in permanent marker, so you will remember in future which is which.

Getting housemates to comply is a separate problem.