Before you write your poem, brainstorm based on these questions: who did you encounter everyday at lunch in school? This can include friends, teachers, cafeteria workers, or even enemies. How did you feel both before and after lunch time? What did you eat? Was there a day you can remember where something out of the ordinary happened?
This can be something strange, sad, or joyful. You can also, of course, invent a character, answer these questions as that character, and write a poem based on that fictional experience. Poetry never has to be factual, only emotionally true!