Preheat the oven to 375 degrees F (190 degrees C). Lightly grease an 8-inch square baking dish with cooking spray.

Heat a large nonstick skillet over medium-high heat. Add turkey and onion; cook and stir until turkey is browned and crumbly and onion is soft, about 10 minutes. Drain.

Bring a large pot of lightly salted water to a boil. Cook egg noodles in boiling water, stirring occasionally until cooked through but firm to the bite, about 5 minutes. Drain and return to the pot.

While the water is coming to a boil for the noodles, stir tomato sauce and Italian seasoning into turkey mixture. Bring to a boil over medium heat. Reduce the heat to low, cover, and simmer for 10 minutes.

At the same time, combine milk, cream cheese, parsley, and garlic in a small saucepan over medium heat. Cook, stirring occasionally, until cream cheese melts, about 5 minutes. Pour over egg noodles and stir to combine. Transfer to the prepared baking dish.

Layer turkey mixture over noodles. Sprinkle mozzarella cheese over top.

Bake in the preheated oven until casserole is hot and cheese is melted, 15 to 30 minutes.