Remove stems from tomatoes. With the tip of a sharp knife, pierce tomatoes. Carefully insert a sliver of garlic into each tomato.
Place tomatoes in the center of a 18x12 sheet of foil. Drizzle tomatoes with the olive oil; sprinkle with rosemary, parsley, sugar and salt. Bring the two long sides of the foil together and seal with a double fold. Fold remaining edges together to completely enclose tomatoes.
Grill tomatoes on the rack of a grill directly over coals or gas burners for 4 to 5 minutes or until heated through. Or bake in a preheated 350*F. oven for 4 to 5 minute or until heated through.
To serve, carefully open foil packet(watch out for hot steam!). Move tomatoes to a serving platter. Sprinkle with salt and serve immediately.