How to Make It
Preheat grill to medium-high (400°F to 450°F). Stir together basil, cilantro, mint, and chives in a small bowl. Cut zucchini and yellow squash lengthwise into 1/2-inch-thick slices. Place in an even layer on a rimmed baking sheet; drizzle with oil, and sprinkle with 3/4 cup of the herb mixture. Sprinkle with salt and pepper, and let stand 10 minutes. Place squash slices directly on oiled grates, and grill, uncovered, turning occasionally, until lightly caramelized, about 10 minutes.
Transfer squash to a serving platter. Sprinkle with remaining 1/4 cup herbs, and drizzle with vinegar.