One of the best ways to have good conversations with your teen about healthy eating is to cook together. Whether it's a discussion about the benefits of whole wheat over white while kneading pizza dough or the virtues of fruits and veggies while dicing carrots for stir-fry, your child is bound to absorb a lot more while involved in the cooking process.
If you're too busy to do much cooking, why not form a teen cooking group with other parents and their children? Establish a weekly cooking night and parents can take turns being the host. Make sure that the other parents share your values about healthy foods ahead of time!