1/2 cup fresh flat-leaf parsley leaves, finely chopped, plus more, for garnish
1/4 teaspoon freshly grated nutmeg
1 butternut squash (about 2 1/2 pounds), peeled, seeded, halved lengthwise and cut into 1/4-inch-thick half-moons
2 cups shredded part-skim mozzarella
Set the oven to 400 degrees Fahrenheit. Lasagne noodles should be soaked in warm water.
In a big skillet over medium heat, warm the oil. Add the salt, pepper, garlic, and onions. About 10 minutes of cooking time, with occasional stirring, should result in soft, caramelized vegetables. Add one or two tablespoons of water if the mixture starts to feel too dry.
In the meantime, combine the cornstarch and 1/2 cup of milk in a small basin and whisk to combine. In a big saucepan, warm the remaining 3 1/2 cups of milk until it begins to bubble. Bring the milk to a boil while incorporating the cornstarch mixture. About 5 minutes of simmering and stirring will get the milk to the consistency of the thin batter. Add the spinach, parsley, nutmeg, and onion combination and stir until the spinach wilts. Add salt and pepper to taste. Get rid of the heat.
Naan should be drained. In the bottom of a glass or ceramic baking dish measuring 13 by 9 by 2 inches, spread 1 cup of the spinach mixture. Put three lasagna noodles on top of the spinach. Sprinkle one-third of the mozzarella cheese over the noodles after placing half of the squash on top, gently overlapping. Place 3 noodles, the remaining squash, and a third more of the mozzarella on top of the cheese after spooning 1 cup of the spinach mixture over it. The final 3 noodles are placed on top, then the remaining 1 cup of the spinach mixture. Wrap foil up securely and set aside the remaining mozzarella.
For 40 minutes, bake. Remove the lid, then top with the remaining mozzarella. Bake for about 15 minutes, or until bubbling and the squash is soft. Before serving, let stand for at least 10 minutes.