A sprinkling of sugar and then a few minutes on the grill transforms good tomatoes into great ones. To grill scallions, tie them in bundles using twine soaked in water. This will prevent them from slipping through the grate.
I made this with ahi tuna, corn, and mangoes also on the grill, and used olive oil and a grill seasoning instead. The timing is quite far off from what I can do on my little kettle grill, and the tomatoes are especially taking a lot longer, but it's well worth my wait. When you need something different on the grill, this is the way to go. It is as easy as it is tasty!