Thickly slice the eggplant, and lay the rounds on cake racks which you've placed in the sink. Salt, very generously, and leave 30 minutes for the excess water to drain off. When they are ready, rinse them well under the tap and pat them dry with a towel.
While the eggplant drains, put the red and yellow peppers in the oven and broil to blacken the skin on all sides, 20 minutes total. Remove to a bowl, cover with plastic wrap, and let sit 5 minutes. The skin will now peel off easily. Peel and seed, then slice the flesh to julienne and put it in a large bowl.
Turn the oven down to 450 degrees F.
Put some oil on a baking sheet and toss the zucchini slices in it. "Grill" in the oven, turning once, about 10 minutes. Remove, and add to the peppers. Finally, cut the rinsed and dried eggplant into large chunks, toss in oil, and spread on the baking sheet, and "grill" also, about 15 minutes. As things are done, add them to the bowl.
While the vegetables are in the oven, heat a spoonful of olive oil in a saute pan, and fry the onions until soft. Add the garlic, pepperoncini, bay leaf, and rosemary, and saute 1 minute. Add the tomatoes. Cook the tomatoes until they are very soft and the whole mixture thickly soupy, about 15 minutes.
Pour the tomato over the vegetables, and toss everything. Check the seasonings. Serve at room temperature with the basil scattered over.