Contrary to other answers on your question, I have to say that your guest would most probably be disappoint, but would commend you for your effort.
Any food prepared in a non-kosher utensil would make that food non-kosher. Having said that, there are some guidelines you might follow:
The easiest way around your problem is to serve a cold salad, if possible on a glass dish or better yet, not being too fancy on paper plates with good quality plastic utensils.
Hard boiled eggs still in the shell are ok. served with a cold salad. Cans of tuna fish or salmon, but NO Shell fish.
You might look for prepared products bearing labels that indicate the product is kosher, and better still, that the product is micro-wave able.
If you need more guidance, please repost and I will attempt to clarify any questions you may have.
Good luck.
The Nosher