Vegetable Tian

head garlic, separated into cloves with all but 1 clove unpeeled

olive oil

yellow squash, about 6 ounces, thinly sliced crosswise

small Japanese eggplant, about 6 ounces, thinly sliced crosswise

zucchini, about 6 ounces, thinly sliced crosswise

plum tomatoes, about 1 pound, sliced lengthwise ¼-inch thick

medium red onion, thinly sliced crosswise

Coarse salt and freshly ground pepper

Sprigs of thyme, rosemary, oregano, or marjoram