Put 2 cups of salted water and the vinegar in a large, stainless steel saucepan and bring to a boil. Slice 1-inch off the tops of the center cone of the artichokes and cut the stalks so they will sit flat. Trim the tips from the leaves and rub the surfaces with lemon. Put the artichokes in the water and simmer, covered, for about 30 minutes. When the leaves pull off easily, put the artichokes on a rack; cool and drain them upside down. Remove the center leaves and the choke with a spoon and discard.

Saute the onion in 1 tablespoon of olive oil, stirring until translucent, 3 to 5 minutes, then transfer to a bowl. Saute the zucchini in the remaining olive oil until lightly browned, add the mushrooms and cook for 2 more minutes, add to the onions.

Mix the egg, mozzarella, lemon juice, and 1/2 cup of Parmesan. Add to the vegetable mixture, stir well.

Heat the extra virgin olive oil in a saucepan and add the garlic and the bread crumbs. Brown lightly. Remove from heat and stir in the vegetable-egg mixture. Stuff the center and the leaves of the artichokes with the mixture. Set the artichokes upright in a baking dish with the water below the first leaf, about 1 cup. Sprinkle the juice of one lemon and the remaining Parmesan over the artichokes. Bake them, covered, for 30 minutes. Uncover for the last few minutes to brown the cheese.