My office had this same "green food" theme for our pot luck lunch last week. I am limited as to what I can bring because I commute via bus, but this is what I brought.

Prepare one box of lime jello (I used diet) per box directions. When partially set, add some crushed pineapple, crushed walnuts, and small marshmallows. What you add to your jello can vary such as a different fruit, or omission of any of the items I added. Stir to mix & return to the refrigerator to set. Can be served with a dollop of whipped cream on top.

Today the bar where I get my soup du jour is serving split pea soup, so I'm having green food today, also!