Rigatoni, Cheese & Pea Casserole (Pasticcio di Rigatoni e Piselli)

Preheat oven to 350°F. Coat a 3-quart baking dish with cooking spray. Coat dish with 1/4 cup breadcrumbs, tapping out the excess. Put a pot of water on to boil for cooking pasta. Heat 1 tablespoon oil in a heavy medium saucepan over medium heat. Add flour and cook, whisking constantly, for 1 to 2 minutes. Add hot milk and bring to a simmer, whisking, until smooth and slightly thickened, 3 to 4 minutes. Add nutmeg. Season with salt and pepper. Transfer to a bowl; set aside to cool. Heat remaining 1 tablespoon oil in a large nonstick skillet over medium-high heat. Add onion and sauté until softened, about 5 minutes. Add peas and cook for 4 minutes longer. Season with salt and pepper. Add to the milk mixture. Meanwhile, cook rigatoni (or ziti) in boiling salted water until al dente, 8 to 10 minutes. Drain and rinse well. Toss with reserved sauce and vegetables. Stir in fontina. Spoon the pasta mixture into the prepared baking dish. Mix remaining 1/4 cup breadcrumbs and Parmesan in a small bowl. Sprinkle evenly over the pasta. Bake pasta until golden and bubbly, 30 to 45 minutes. Let stand for 10 minutes before serving.