I stuck the walnuts in my skillet and toasted them for a bit. I suppose this would be optional...
Whizz everything (except the cherry tomatoes, obviously) together in your food processor. Adding the olive oil a li'l at a time.
I put it in the fridge for a while, where it sorta solidified. Ish.
Cut the tomatoes in half and scoop out the insides so you have li'l cups.
Put in about half a teaspoon or whatever of the pesto inside each half. Squash it down with your thumbs and stick it on a tray lined with foil.
Grill for about 5 or 10 minutes.