Source: https://www.seriouseats.com/grilled-ratatouille-recipe
In a small bowl whisk together 2 tablespoons oil, vinegar, garlic, basil, marjoram, and thyme. Season with salt and pepper to taste; set aside.
Place tomatoes, zucchini, yellow squash, eggplant, onion, and bell peppers on a large rimmed baking sheet. Drizzle remaining 1/4 cup oil over vegetables and season with salt and pepper to taste. Toss to thoroughly coat vegetables in oil and seasoning.
Light one chimney full of charcoal. When all charcoal is lit and covered with gray ash, pour out and spread the coals evenly over entire surface of coal grate. Alternatively, set all the burners of a gas grill to high heat. Set cooking grate in place, cover grill and allow to preheat for 5 minutes. Clean and oil the grilling grate. Place vegetable slices on grill and cooked until browned on both sides, about 3 minutes per side for zucchini, squash, and eggplant, about 5 minutes per side for tomatoes, onion, and peppers. Transfer vegetables to cutting board and cut into large dice.
Transfer vegetables to a large bowl, pour in herb vinaigrette and toss to combine. Serve immediately while warm or at room temperature.
By Alex Gibbons