Prepare an outdoor grill with a hot fire.
Grill the tomato and garlic halves, turning as needed, until charred all over, about 6 minutes. Set garlic aside. Wrap tomato in foil and set aside.
Brush the zucchini, yellow squash, eggplant slices, and pepper strips generously with the 1/2 cup olive oil. Season with 1 tablespoon salt and black pepper to taste. Grill the vegetables over direct heat until "kissed by the grill" and just tender, 2 to 3 minutes per side.
Chop the tomato and put it in a large bowl, along with the skin and juices. Squeeze the garlic from its skin, chop, and add to tomato. Dice the rest of the vegetables into large pieces and add to tomato. Drizzle with the remaining 1 tablespoon olive oil, vinegar, basil, and thyme. Season with salt and pepper to taste and toss gently, taking care not to overwork the vegetables. Serve warm or at room temperature.
Know-How: The shot of white wine vinegar at the end brightens the flavor of the ratatouille and cuts through the smoky taste of the grill. Add it according to your taste to balance the char flavor from grilling.
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