Go to dinner. Ask questions. If they try to change the subject or rephrase your question into something you didn't really ask, don't let them get away with it, repeat the question without rephrasing it into something they might like better. The more they want to weasel their way out of answering your question, the more important it is that you get an honest answer from them.
And look them in the eyes when you ask. Don't feel that they have the moral high ground because they belong to their 'one true religion' with promises of salvation and you are just a lowly non-believer who will be destroyed at BalmyGeddon if you don't join in the very near future.