Cut off the top quarter of each onion, round zucchini, and tomato. Hollow out all the vegetables (except peppers and flowers) with the help of a spoon or small knife, leaving a thick wall. Save the tops and carved-out parts and chop.
In a saucepan, immerse the hollowed-out halved eggplants in the 12 cups of salted water (unheated). Allow to soak while stuffing is prepared.
In a skillet heat 1/3 cup olive oil on a low flame and saute the reserved chopped vegetables until just tender, stirring lightly and frequently. In a large bowl combine the fresh bread crumbs and milk, and allow to soak briefly. Then add the Sauteed vegetables, sausage meat, garlic, chopped parsley, basil, beaten eggs, Parmesan, salt, and pepper. Mix well.
Remove the eggplant from the water. Bring this water to a boil and briefly blanch the vegetables separately in this order: white onions, zucchinis, peppers, eggplant (not the tomatoes or stuffed zucchini blossoms). Drain them on a clean towel or paper towel.
Spoon the sausage stuffing into each vegetable, then sprinkle with bread crumbs. Arrange in a baking dish that has been oiled on the bottom with olive oil. Bake uncovered in a preheated 400 degree F oven for about 15 to 20 minutes. For each person, arrange 1 piece of each kind of vegetable on a plate.
Optional: For a true Provencal touch (and if they are available) prepare Stuffed Zucchini Blossoms and add one to each plate.
In a skillet with 2 tablespoons olive oil, saute the finely chopped zucchini 5 to 8 minutes on a low flame. Remove from the heat and add parsley, basil, garlic, salt, and pepper. Let cool, then add breadcrumbs and the beaten egg. Mix well.
Preheat oven to 400 degrees F.
With the fingers, partially open each blossom's petals and place a spoonful of stuffing inside. Carefully close the petals. Put the stuffed blossoms side by side in a shallow roasting pan. Dissolve the bouillon cube in the boiling water and add the remaining olive oil. Pour liquid over blossoms and cover with aluminum foil. Bake for approximately 20 minutes. Arrange on a dish. Can be eaten hot or cold.