You just need a good-quality bread (found at your local bakery) such as Fione, pesto (which can be found pre-made at grocery stores), and organic tomatoes & mozzarella cheese.
If you have a panini maker, use that, but I have a miniature grill that worked just fine. Maybe if you're adventurous you can even try it on your stovetop.
Slice 2 pieces of bread. Spread pesto on one and top it with tomato and cheese slices. Put the other half of bread on top like a sandwich. Then, toast it until golden brown!