Lemon or lime juice and a little salt go a long way towards reducing the odour of both garlic and onion on your chopping board.
Sprinkle your cutting board with salt. Cut a lemon or lime into quarters and use these quarters to rub the salt into the board, squeezing the juice on to the board as you go. Let the board sit for two to three minutes, and then wipe it clean with a damp cloth.
Voila....odour free cutting boards.