Preheat oven to 375F and move the rack to the middle position.
Cook the pasta for 2 minutes less than package directions indicate. Once cooked, drain and add to a greased 9x13 casserole dish.
Meanwhile, add the oil and butter to a skillet over medium-high heat. Sauté the onion and mushrooms until the mushrooms have released their water and it's cooked out and everything is nicely browned (about 8 minutes).
Stir the garlic in and cook for about 30 seconds.
Stir in the pesto and cream and once the sauce starts to bubble, cook for about 2 minutes or until it's slightly thickened (don't let it get too thick as it'll thicken more in the oven). Take the skillet off the heat.
Stir in the turkey and some salt & pepper to taste.
Transfer the skillet mixture to the casserole dish, add half the cheese, and toss.
Top with the rest of the cheese. (Note: if you want it extra cheesy, feel free to add more than the suggested 1 cup on top.)
Cover the casserole dish with foil and bake for 20 minutes or until it's warmed through.
Take the foil off and broil the top for a few minutes if you want to brown the cheese (optional). Watch that it doesn't burn!
Let it sit for a few minutes prior to serving. Sprinkle with chopped parsley if using.