I made this ahead, so I baked it in the oven early in the day, then re-warmed it on the barbecue when we were cooking our burgers. You can also do the whole thing on the barbecue, just give it a good half hour and don't chop your potatoes too big.
To make ahead, roast potatoes, onion and bacon, let cool to room temperature, then transfer to airtight container or Ziploc bag and store in the fridge for up to 3 days. When ready to serve, toss with herbs, tomatoes and dressing, wrap in lightly-greased foil or place on foil in large grill basket, and heat on barbecue or in oven for about 20-30 minutes, until hot through. Leftovers taste great warm or cold.