Bring a large pot of lightly salted water to a boil. Cook pasta in boiling water for 8 to 10 minutes, or until al dente; drain.
Preheat oven to 425 degrees F (220 degrees C).
In a large bowl, thoroughly mix noodles, onion, 1 cup cheese, peas, tuna, soup and mushrooms. Transfer to a 9x13 inch baking dish, and top with potato chip crumbs and remaining 1 cup cheese.
Bake for 15 to 20 minutes in the preheated oven, or until cheese is bubbly.
