Preheat oven to 350 degrees F (175 degrees C). Grease a 2 quart casserole dish.
Bring a large pot of salted water to a boil, add noodles, and cook until al dente; drain.
In a large mixing bowl, combine noodles, tuna, celery, and green onion. Stir in sour cream, mustard, and mayonnaise. Season with salt and thyme.
Spoon 1/2 of the noodle mixture into the prepared casserole dish. Top the casserole with cheese.
Bake in preheated oven for 30 minutes, or until hot and bubbly. Sprinkle with crumbled french fried onions. Bake for 5 minutes more or until golden brown.