- 2 tablespoons balsamic vinegar
- 1/2 cup extra-virgin olive oil
- 2 teaspoons finely chopped fresh thyme
- 1 teaspoon finely chopped fresh basil
- 2 large red onions, halved, thinly sliced
- 1 yellow bell pepper, cut into 1/2-inch-wide strips
- 1 red bell pepper, cut into 1/2-inch-wide strips
- 1 orange bell pepper, cut into 1/2-inch-wide strips
- 1 1-pound eggplant, quartered lengthwise, cut crosswise into 1/2-inch slices
- 1/2 pound yellow squash (about 2 medium), cut into 1/3-inch-thick rounds
- 1/2 pound zucchini (about 2 medium), cut into 1/3-inch-thick rounds
Whisk vinegar and mustard in medium bowl. Gradually whisk in oil. Stir in garlic, thyme, and basil. Season to taste with salt and pepper. Do Ahead: Dressing can be made 1 day ahead. Cover and chill.
Preheat oven to 450°F. Toss onions and next 6 ingredients in large bowl; sprinkle with coarse salt and pepper. Add dressing; toss to coat. Divide between 2 large rimmed baking sheets. Roast until vegetables are tender and slightly brown around edges, about 35 minutes.