In medium bowl, whisk together pumpkin, eggs, cayenne, and 1/4 teaspoon each salt and black pepper. Set aside.
Heat large pot of salted water to boiling over high heat. Add pasta and 1 tablespoon oil and cook as label directs. Drain pasta; set aside.
Return same large pot to stove. Add remaining 2 tablespoons oil, garlic, kale (in batches, if necessary) and red pepper flakes. Cook 2 to 3 minutes or until all kale is slightly wilted. Remove from heat and set aside.
In medium saucepot, melt butter over medium heat. Add flour; cook 1 minute, whisking constantly. While whisking, slowly add milk. Cook 6 to 8 minutes or until slightly thickened, whisking constantly. Remove from heat; stir in sage, nutmeg, and remaining 1/2 teaspoon salt and 1/4 teaspoon black pepper. Set aside.
Preheat oven to 350 degrees F. Spray lasagna pan or large baking dish with nonstick spray. Pour about half of cream sauce in bottom of dish. Add layer of noodles, then spread noodles with half of pumpkin mixture. Add another layer of noodles, followed by half each of the mozzarella and Parmesan. Add all of the sauteed kale. Sprinkle kale with all of the couscous. Add layer of noodles. Spread noodles with remaining pumpkin mixture. Spread all of the sausage slices (if using) over pumpkin. Top sausage with remaining mozzarella. Add one last layer of noodles. Pour remaining cream sauce over everything. Sprinkle with remaining Parmesan.
Cover with foil and bake 30 minutes. Remove foil, bake 15 minutes longer or until edges are bubbly. Let rest 15 minutes before serving topped with parsley, if desired.