Preheat oven to 375°F and grease a casserole dish.
Cook egg noodles according to package directions, drain and set aside.
In a large skillet, sauté mushrooms in 1 tablespoon butter until tender. Set aside.
In a large bowl, mix together cooked noodles, drained tuna, cream of chicken soup, sour cream, and sautéed mushrooms.
Gently fold in drained peas to avoid crushing them.
Season mixture with salt and pepper to taste.
Transfer mixture to prepared casserole dish.
Melt 1/2 cup butter and mix with crushed Ritz crackers.
Sprinkle cracker mixture evenly over the top of casserole.
Bake for 30 minutes until crumbs are golden brown and casserole is bubbly.