If the grill is hot, why not roast the vegetables?
makes about 2 cups

6 small ripe tomatoes (about 1½ lb.), halved and cored
2 ears fresh corn, husked
½ small onion, peeled and halved
3–5 garlic cloves, peeled
3 jalapeños, stems removed
1 Tbsp. lemon juice
1 tsp. sea salt

Wipe the grill grate or griddle with high-temperature oil and set the heat to medium-high. When the grill is hot, place tomatoes and onion directly on the grate, and the garlic and jalapeños in small cast-iron skillet on the grate. Roast about 2–4 minutes, then turn vegetables over. Watch each ingredient carefully and remove just before each begins to char.

Transfer tomatoes, onions, garlic, and jalapeños to a food processor and pulse until coarsely chopped. Transfer mixture to a bowl and cut the corn off the cob straight into the bowl. Add lemon juice and salt; mix well and serve.