To make your dressing, add the garlic and lemon zest and juice to a large bowl. Pour in 3 times the amount of extra virgin olive oil and add the finely chopped parsley stalks. Mix together.
If you've got them, throw your herb branches on to the barbie so that they smoke.
Drain your shellfish, then throw them onto the hottest part of the barbie. I like to put a large metal bowl or a deep roasting tray over the shellfish at this point, so they're roasting as well as smoking.
After 3 minutes use a pair of tongs to carefully lift up the side of the tray and check the shellfish have opened. Remove them to the dressing bowl, saving the lovely liquid inside as you do so. Chuck out any shellfish that haven't opened.
Sprinkle over as much chopped parsley and chilli as you like and gently mix everything together. This is wonderful finger food. I use one of the half shells to slurp up the juices. Don't forget paper towels and maybe even a finger bowl.