1. Heat the oven to 150°C.
2. Add all the pesto ingredients (except for the salt, pepper and lemon juice) into a food processor or hand blender. Process until you have a reasonably smooth mixture (you still want it to be a little bit chunky). Season to taste with salt, pepper and lemon. You now have a perfect pesto.
3. Spread a thin layer of the pesto on the bread before adding thin slices of cheese. Close with another slice of bread.
4. In a little oil, fry each sandwich on each side until golden. This will only take a short time, but make sure the cheese is completely melted, it should then have a couple of minutes in the oven.
If you are making lots of sandwiches, then reduce the oven temperature to 110-120°C. Then it will keep them hot.