• Preheat the oven to 350°F and grease a 9x13-inch casserole dish.  
• Fill a large pot with salted water and bring to a boil over high heat.  Add the pasta and cook according to manufacturers’ instructions, to al dente.  Drain the pasta and toss with the olive oil.  Cover the pot and reserve.
• While the pasta is cooking, set a large skillet over medium heat and melt 1 tablespoon of the butter.  Add the sliced mushrooms and cook until they release their liquid and it almost evaporates, add the chopped onions and cook until the onions are soft. Stir in the garlic and cook for 30-seconds.   Transfer the mixture to a plate and set aside.
• Melt the remaining butter in the skillet set over medium heat.  Stir in the flour and cook for 2-3 minutes or until lightly browned.  Whisk in the milk, cream, chicken broth, and wine.  Bring to a gentle boil then reduce the heat to medium-low and simmer, stirring continually until the sauce thickens, about 8 minutes.
• Stir in the thyme leaves. Taste the sauce and add salt and pepper as needed.
• Add the reserved pasta, mushrooms mixture, turkey, sun-dried tomatoes and the thawed peas to the sauce, stirring until evenly coated.  Add the Gruyere cheese, toss gently to fully combine. 
• Transfer the pasta mixture to the prepared casserole dish and spread evenly.  

For the Topping:

• In a small dish, combine the Panko bread crumbs and the Parmesan cheese.  Sprinkle evenly over the top of the tetrazzini and transfer to the oven.
• Bake the tetrazzini for 30 minutes, until it is bubbly around the edges and the top is golden brown.  
• Remove from the oven and allow to sit for 10 minutes before serving.  ‘