Slice your tomatoes, and some fresh mozzarella. We used buffalo mozzarella, but you could use what's available. (But please, not that low-moisture kind.) Or make your own.
For an appetizer for two, (or a meal for one!) we used three beefsteak tomatoes, two balls of mozzarella, and a few sprigs of basil. It's good to let it sit for a bit, and let the oil and balsamic and tomato juices marinade together. Then devour it.