Cut the ends off the cremini mushrooms. Then, evenly slice them. Also, dice the onion.
Add the olive oil to a skillet over medium heat on the stove. Then, add the sliced diced onion to the skillet. Sauté the onions for about 3-4 minutes, until translucent. Then, add the sliced mushrooms, Italian seasoning, garlic powder, salt, and pepper to the skillet. Sauté for an additional 4-5 minutes, until the mushrooms are softened and cooked. After that, remove the skillet from the heat.
In a large bowl, combine the cream of mushroom soup, milk, soy sauce, and sautéed ingredients. Then, add the frozen green beans and thoroughly mix until everything is well combined.
Lightly spray a casserole dish with olive oil. After that, pour the green bean mixture into the dish, spreading it evenly.
Cover the casserole dish with foil and bake it at 350°F for 30-35 minutes.
Make The Topping: In a separate bowl, mix the panko breadcrumbs, Parmesan cheese, Italian seasoning, garlic powder, onion powder, salt, and pepper.
Once done baking, remove the foil from the baking dish. Next, evenly sprinkle the breadcrumb mixture over the casserole. Then, lightly spray the top with olive oil to help it crisp up.
Bake the casserole for an additional 15-20 minutes, or until the topping is golden brown. Once done, let the casserole slightly cool before serving.