This explanation comes from two elements in the dream, namely, dead relatives and chopped green onion. The deceased relatives represent your deep thoughts and feelings, and cutting onions represents psychological catharsis and emotional release. So this dream can be regarded as a way of psychological counseling, allowing you to release your inner feelings in your dream.
If you often dream about your dead relatives, or this dream bothers you, you can take some measures to ease your mood. For example, you can express your thoughts and feelings by keeping a diary or communicating with relatives and friends. In addition, you can also participate in some psychological counseling activities, such as yoga or meditation, to ease your mood.
In short, dreaming of a deceased relative cutting onions represents your thoughts and nostalgia for your loved ones. It is a way of psychological counseling, and some measures can be taken to relieve emotions.