How you contribute to diversity sounds like a tricky topic, but you can actually apply it to a bunch of things. Maybe talk about eccentric family traditions, community you were brought up in, if you are from a different culture, decided to start something new at your school, took the initiative and spearheaded something never done before. You can really use any of these as a theme of diversity, it's all about how you describe it in an essay. Jot down ideas and build from it, think of all the ways that you can bring something new, vibrant, fresh to the Lehigh campus. If you need help, just write down some of the starting ideas and maybe someone on here can help you collect ideas.
Colin Toner