Boil the pasta noodles as directed. Drain well and return to saucepan.
In a large skillet, melt the butter and whisk in the flour. Whisk in the milk and whisk vigorously until flour "melts" into the milk. Whisk in the chicken broth. Bring to bubbling and then stir in the sour cream and cheese. Cook over medium-low heat until sauce bubbles and begins to thicken. Stir in the tuna, garlic powder and salt and pepper to taste.
Add the sauce to the cooked noodles and toss well.
Prepare frozen corn or green beans.
Serve Cheesy Tuna Noodles with vegetable.