Boil the egg noodles in salted water for 2 minutes less than the package directs, then drain them well.
Melt the butter in a skillet over medium-high heat and cook the mushrooms for 6 minutes until browned and dry.
Stir in the flour for 1 minute, whisk in the milk, salt and pepper and simmer for 4 minutes until thickened.
Fold in the tuna, peas, cheddar and noodles and spread the mixture in a greased 9-by-13-inch baking dish.
Cover evenly with crushed potato chips and bake at 375°F for 20 minutes until bubbling at the edges.