Preheat oven to 350 degrees. Lightly spray a 9×9-inch baking dish with cooking spray.
Cook pasta al dente according to package directions. Drain. Set aside.
In the meantime, In a large microwave-safe bowl, add butter, onions, and mushrooms and cook in a microwave for 4-5 minutes, until soft.
To the same large bowl of cooked onions/mushrooms, add chicken, condensed can of soup, ricotta cheese, chicken broth, and yogurt. Add salt, pepper, and garlic powder, to taste. Using a rubber spatula, mix well until all incorporated. Stir in cooked pasta. Mix completely until well tossed.
Pour mixture into prepared baking dish. Top with both kinds of cheese. Cover with aluminum foil. Bake covered for 30 minutes. Remove foil and bake an additional 30 minutes, until cheeses are melted.
Remove from oven and cool for a few minutes. Cut into 6 slices. Any leftovers freeze great!