1. Preheat the oven to 400 degrees Fahrenheit.

2. Pour some of the olive oil to cover the bottom of a 9 x 13-inch rectangular or 12-inch oval baking dish. Layer in half of the onion slices and one third of the tomatoes. Generously sprinkle with salt and pepper. Add a layer of eggplant and sprinkle on more salt. Add another third of the tomatoes, the zucchini, garlic, thyme, and the remaining onions. Top with the remaining tomatoes. Press down on the mixture with your hands. Pour over the remaining olive oil. Season generously with salt and pepper. (Don't worry. The vegetables will be piled high but collapse as they cook.)

3. Bake uncovered for 1 1/2 hours. After 45 minutes, press the mixture down firmly with a spatula. The vegetables should be reduced in height, and should be brownish black and caramelized, almost charred in places. Return to the oven to finish roasting. Let cool for at least 10 minutes, so the mixture can solidify a bit. Cut into squares and serve.