If you see onions in your dream, then you want to pay very careful attention to the details surrounding it. What situation do you see the onion in? This is a situation in your life that has multiple layers that you may or may not have considered. In order to get to the bottom of the onion, and of the layers, you may need to do some work to peel those away.
There also may be a secret in your life, either that you are hiding, or that someone else is hiding, that the onion represents. The secret may simply be a revelation of sorts that you need to be inspired by in order to move forward in your life. You also might dream that an onion makes you cry. If this is the case, the symbol suggests that you are lacking authenticity in your life. You may be showing emotions to someone that are not genuine, and you may need to be a little more real in order to get where you want to in this situation, or even in life.