Place beans in a Dutch oven and cover with water; bring to a boil. Cover and cook for 3-5 minutes or until crisp-tender; drain and set aside.
Preheat oven to 400°. In a large skillet, saute mushrooms in butter until tender. Stir in flour, onion and pepper until blended. Gradually stir in milk. Bring to a boil; cook and stir 1-2 minutes or until thickened. Remove from heat; stir in sour cream and Worcestershire sauce. Stir in beans and cheese until blended.
Transfer to an 11x7-in. baking dish coated with cooking spray (dish will be full). Combine topping ingredients; sprinkle over the top.
Bake, uncovered, 12-16 minutes or until bubbly and heated through.
Test Kitchen Tips
Instead of snapping off the ends of each green bean like Grandma did, trim a bunch in seconds. Gather beans in a small pile, lining up the tips on one side. Cut off tips with a single slice using a chef’s knife. Flip the pile over and do the same on the other side.
If you don't have the minced onion on hand, substitute fresh. One tablespoon of dried minced onion equals 1/4 cup minced raw onion.