Heat the olive oil in a skillet over medium high heat and add the onions and garlic. Saute until soft, then add the spinach and butternut squash. Add salt and pepper to taste. Remove from heat and set aside.
Combine ricotta, mozarella, and parmesan cheese in a bowl and mix well.
Spoon a light layer of bechamel sauce on the bottom of a 9 x 13" baking dish. Place 4 lasagna noodles in a layer on top of the sauce.
Add the sauteed vegetables. Place another layer of noodles on top. Add the cheese mixture and spread over the top of the noodles. Add another layer of lasagna noodles.
Add the turkey and pour a light layer of the bechamel sauce over the turkey so it's saucy. Top with another layer of lasagna noodles. Pour remaining bechamel sauce on top and spread to cover all noodles. Cover with a lid or aluminum foil and bake for 45 minutes.
Remove cover and bake another 15 minutes, until bubbly and starting to brown lightly on top.
Heat the butter and flour in a skillet over medium heat, stirring continuously until it becomes a paste. Slowly add the milk, a little at a time until a sauce forms.
Add the salt, pepper and nutmeg. Continue stirring until it starts to simmer and thicken (about 5-10 minutes). Once thick enough to coat a spoon, remove from heat and set aside.