Cook the Pasta: Boil the fettuccine in salted water until just under al dente. Drain and set aside.
Make the Sauce: In a 9x13 dish, whisk together the cream of mushroom soup, sour cream, water, chicken bouillon, onion powder, garlic powder, oregano, and pepper until smooth.
Add the Cheese and Turkey: Stir in the shredded turkey, parmesan, and 1½ cups of the mozzarella until combined.
Combine with Pasta: Add the cooked fettuccine to the sauce mixture and toss until fully coated.
Sprinkle the remaining ½ cup mozzarella on top.
Make the Topping: In a small bowl, mix the melted butter with the Italian-style breadcrumbs until evenly moistened.
Add the Topping: Sprinkle the breadcrumb mixture evenly over the tetrazzini.
Bake: Bake at 350°F for 20–25 minutes, or until golden and bubbly around the edges.
Serve: Let rest for 5 minutes before serving. Creamy, cozy perfection.