1In a gallon-size re-sealable plastic bag, marinate onions, zucchini and eggplant in ¼ cup olive oil, 1 tablespoon basil and 1 teaspoon both salt and pepper (careful not to break up onions). Set aside.
2Create burgers by placing sausage and turkey into a large mixing bowl and with hands, thoroughly combine. In a small mixing bowl, combine next 9 burger ingredients along with 1 teaspoon both salt and pepper. Add small bowl ingredients with turkey and sausage mixture and mix well to incorporate. Cover with plastic wrap or foil and set aside in refrigerator for spices to merry, at least for 30 minutes.
3Prepare gas grill on medium-high heat. Divide burger mixture into 6 equal portions (about 1-inch thick burgers). Place the slices of prosciutto on a cutting board or piece of wax paper. Place one burger patty in center of prosciutto and wrap prosciutto around burger. Repeat with remaining burger patties.
4Along with marinated vegetables, cabbage wedges, bell pepper and tomatoes, place burgers prosciutto-ends-touching side down on grill over medium-high heat. Drizzle vegetables with remaining olive oil and sprinkle with 2 tablespoons basil. Grill vegetables for 6 to 8 minutes on both sides. Grill burgers for 10 to 12 minutes turning once or twice until fully cooked or until turkey is no longer pink in the center, and until the prosciutto is golden. With 2 minutes or so to go in cooking time, place slices of cheese on top of burgers to soften. Remove burgers from heat and set aside. Remove vegetables to cutting board(s).
5When ready to serve, remove core from cabbage wedges and slice along with bell peppers, tomatoes, eggplant and zucchini. Place a bottom hamburger bun onto a plate and lay handful of cabbage. Then layer burger with a burger patty, grilled slices red pepper, onion, tomato, zucchini, and eggplant along with sprinkle of sliced cabbage. Cover with top bun smeared with teaspoons of hummus. Repeat for remaining burgers, creating 6 burgers. Serve immediately.