I love grilled zucchini and squash with burgers. I normally just slice them, put them in tin foil with a little butter and pepper and put them on the grill for about 45 minutes.
I know for this particular event tomatoes would be an issue, but one of my favorite things to toss together is a couple of cartons of grape tomatoes, an equal amount of mozarella balls, some pitted calamata olives, snipped basil and olive oil.
Joyce