Preheat oven to 425°F (220°C). Lightly oil a 9 x 13 inch (22 x 33cm) baking dish. In a large skillet, on medium, heat oil. Add onions and sauté until soft. Add garlic and seasoning and sauté a few minutes more. Add ground turkey. Sauté until meat is cooked and starts to brown. Season with salt and pepper to taste. Add stock, tomatoes, mushrooms and zucchini. Bring mixture to a boil and cook covered for 5 minutes. In a bowl, blend ricotta cheese, ½ cup fontina cheese and mozzarella cheese. Set aside. Cook ziti in salted boiling water until ad dente*. Drain pasta but do not rinse. Toss warm pasta with cheese mixture. Add turkey mixture and toss again. Pour pasta into baking dish and sprinkle with remaining ½ cup fontina cheese and breadcrumbs. Bake for 20 minutes until cheese is melted and golden.
*Ad dente means "to the tooth" or slightly undercooked/slightly firm to the bite.