Preheat your oven to 375 degrees
Bring a large pot of salted water to a boil and cook 12 ounces of pasta for 1-2 minutes less than manufacturer’s directions so it is just al dente. Drain, cover with a towel and set aside for now
Add 2 tablespoons of butter into a large skillet over medium heat
Add 16 ounces of sliced mushrooms and diced yellow onion and cook until softened
Add 3 cloves of minced garlic and cook for 60 seconds
Add 4 tablespoons of butter and once the butter has melted, sprinkle 1/4 cup of all purpose flour over the butter, whisk to combine and cook for about 60 seconds or until the flour slightly deepens in color
Add 1 1/2 cups of stock and a quart of half and half and whisk to combine
Add 2 teaspoons of dried Italian herbs, a generous pinch of salt and black pepper and a small pinch of nutmeg and continue cooking until the mixture begins to form small bubbles around the edges of the skillet
Remove the skillet from the heat and add 1 cup of finely shredded parmesan, 1 cup of frozen peas, 4 cups of shredded turkey and the cooked pasta and carefully mix until everything is evenly distributed
Note: if baking on a separate dish, transfer the mixture into that dish now
In a small bowl, combine 3/4 cup of panko breadcrumbs with 1/2 cup of grated parmesan and add 2 tablespoons of melted butter and evenly spread the mixture over the casserole and cover the dish with foil
Bake in a 375 degree oven for 25 minutes, remove the foil and bake for another 10 minutes or until the breadcrumbs are golden brown
Allow the casserole to rest for a few minutes before serving
Garnish with fresh parsley