Bring a large pot of light salted water to a boil. Cook pasta in
boiling water for 8 to 10 minutes, or until al dente; then drain.

Preheat oven to 425 degrees F.

In a large bowl, mix noodles, onion, 1 cup cheese, tuna, both cans of soup and cut mushrooms. Transfer to pyrex baking
dish, and top with potato chip crumbs and remaining cup
cheese.

Bake for 15 to 20 minutes in the preheated oven, or until cheese bubbles.