Start by preheating the oven to 400 degrees F. Lightly oil a casserole, preferably a 9" oval. At least that's what we used to spectacular results. Scatter the bottom of the dish with 4 cloves of peeled garlic, each clove halved.
You'll need about 2 lbs. of small eggplants such as the Italian variety, around 2 or 3 total. Slice them crosswise in to 1/4" rounds. Do exactly the same with 3 or 4 medium-size onions and 6 medium-size tomatoes. Create three rows of alternating veggies, all standing on their edges - an eggplant slice, a tomato slice, an onion slice, repeat.
Brush the veggies with 2 T. of olive oil and sprinkle generously with salt. Bake for 50 minutes or until the eggplant is really really soft. Remove the pan from the oven and stick, here and there, a few slices of fresh mozzarella between the veggies. Brush again with olive oil, sprinkle with fresh or dried thyme leaves and bake an additional 15 minutes.
Finally, remove from oven and let rest 15 minutes or longer before serving warm or at room temperature. If desired, garnish with grated Parmesan, black pepper and additional salt.