Preheat the oven to 350°F (175°C).
Sauté mushrooms in olive oil.
Mix cooked chicken, sautéed mushrooms, cream of mushroom soup, and sour cream in a large bowl.
Stir in garlic powder, salt, and pepper.
Transfer the mixture to a greased baking dish.
Sprinkle shredded cheddar cheese on top.
Top with breadcrumbs for crunch.
Bake for 25-30 minutes or until the bubbling and golden.
Let it cool for a few minutes before serving.