While we're on the topic of tomatoes and barbeques, the two go together like, well, tomatoes and barbeques.
Just slice them up, sprinkle with freshly ground salt and pepper, fresh grated parmesan, olive oil and fresh thyme leaves.
Pop them on the back of the barbeque and let them sit there and cook while the main event is taking place around them.
That's all there is to it. Enjoy.