Preheat the oven to 350℉ and spray a 9x13-inch casserole dish. Set aside.
Bring a large pot of salted water to boil. Cook the linguine noodles to al dente, for about 9 minutes. Strain and set aside.
Heat the avocado oil in a large skillet over medium/high heat. Add the mushrooms and onions and cook until the onions are translucent and the mushrooms have cooked down to about half the size. About 5 minutes.
Add the garlic to the onions and mushrooms and cook for another minute.
Next, mix in the salt, pepper, and Italian seasoning to the veggie mixture.
Add the butter and flour to the skillet. Let the butter melt and the flour coat all of the veggies. It should look like a thick paste is coating all of the veggies. Cook for one minute.
Whisk in the chicken broth making sure to scrape up the sides to mix in all of the flour and butter paste. Add the cream cheese to the skillet. Using a spatula, break it up into large chunks to help it melt into the sauce.
Next, add the sherry vinegar, heavy cream, and 1 cup of parmesan cheese to the skillet. Stir to combine. Add the chopped-up turkey to the skillet and cook for 5 minutes.
Remove the skillet from the heat and add the frozen peas and the cooked noodles. Mix to combine.
Then, transfer the pasta to the casserole dish. Top the noodles with the remaining parmesan cheese and mozzarella. Bake for 30 minutes.
Allow the tetrazzini to sit for 5 minutes before serving.