Preheat oven to 350 degrees F. In a medium skillet heat oil over medium heat. Add onion; cook for 6 to 8 minutes or until tender. Set aside.
In a large bowl whisk together cream of mushroom soup, cream cheese, milk, garlic powder, and pepper. Stir in beans. Transfer bean mixture to a 1 1/2- to 2-quart casserole or baking dish. Spoon onions over bean mixture, spreading evenly. Sprinkle evenly with panko. Coat panko with cooking spray. Bake about 45 minutes or until heated through and panko is starting to brown.