Vegetable and cheese filling: In a large skillet, heat 3 tablespoons oil over medium heat.  Add scallions and sauté until slightly soft, about 7 minutes. Season with salt and pepper and add bread cubes. Saute for about 10 minutes and set aside. In a separate skillet, heat remaining 2 tablespoons oil over medium heat. Add zucchini and thyme, season with salt and pepper and saute for 7 minutes. Set aside. In a large bowl, combine eggs, ricotta cheese, heavy cream, nutmeg and salt. Add scallions and bread cubes, and mix well.

Prepare dough: Preheat oven to 350°. On a lightly floured surface, roll out puff pastry to a 1⁄10-inch thickness. Transfer to a 9-inch round springform pan, and press with your fingers to line the pan with the dough. Fold overhanging dough back over itself and press firmly, creating a thicker layer on the sides. Trim any excess dough. Spread ricotta mixture and top with cubed cheese. Arrange zucchini in a layer over mixture, and sprinkle with parmesan. Bake for 30 minutes, remove pan from the oven. Carefully remove the ring from around the springform, without breaking the crust. Place pan back in the oven and continue to bake for another 10-15 or until golden brown.