Preheat your oven to 350 degrees.
Spray a 13x9-inch pan with cooking spray.
Boil the noodles per the package instructions (without the salt).
Melt butter in a large skillet on medium heat.
Add onions and cook for 4 minutes.
Add in the frozen vegetable mix and cook for 4 minutes or until thawed.
Stir in the flour until blended and then cook and stir for one minute more.
Slowly add in the milk and bring it to a boil. Continue to stir until the mixture thickens.
Remove from heat.
Stir in the turkey, soup, and sour cream.
Drain the cooked noodles and stir them into the mixture.
Pour the mixture into a greased 9x13-inch pan.
Sprinkle shredded cheese on top.
Cover with tinfoil and bake for 30 minutes. Remove the tinfoil for the last 10 minutes of baking