Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x9 baking dish.
Bring a large pot of lightly salted water to a boil. Add spaghetti, and cook for 8 to 10 minutes or until al dente. Drain, and place back in the pot.
Heat olive oil in a medium saucepan over medium heat, saute onions until tender 5-10 minutes. Add the garlic and saute another minute or two. Add the butter to the pan, once melted whisk in the flour, and cook for 1 minute. Whisk in the turkey stock, milk, nutmeg, pepper, and salt. Cook and whisk until it comes to a boil and starts to thicken. Stir in 1 1/4 cups of Parmesan cheese and remove from the heat.
Stir the turkey, peas and cream mixture into the cooked spaghetti.
Pour into the baking dish, spread out evenly. Sprinkle with the remaining 1/2 cup of Parmesan cheese.
Bake for 25-30 minutes, until bubbly.
Let rest 5 minutes before serving.
Make your own turkey stock it really adds tons of turkey flavor to this recipe.