Preheat oven to 375°F. Prepare a 9x13-inch baking dish with a light coating of nonstick cooking spray.
Heat olive oil in a large skillet over medium heat. Add the onion and cook for 2-3 minutes, until translucent. Add the garlic, celery, and mushrooms. Cook, stirring occasionally, until softened and fragrant, about 5 more minutes. Remove from heat.
In a large mixing bowl, gently toss together the cooked ziti, sautéed vegetables, marinara sauce, Worcestershire sauce, Italian herbs, mascarpone, chopped basil, and half the Parmesan. Season to taste with salt and pepper.
Spread half the pasta mixture evenly into the prepared baking dish. Layer with half the mozzarella slices.
Add the remaining pasta mixture and top with the rest of the mozzarella and Parmesan.
Cover the dish with foil and bake for 20 minutes. Remove the foil and continue baking for 7-10 minutes, until the cheese is bubbling and golden brown.
Remove from oven and let the casserole rest for 5 minutes before serving warm.