Hamburger Hash Brown Casserole

Name: Hamburger Hash Brown Casserole
Ingredients: 2 lbs lean ground beef; 1 small yellow or white onion (diced (approximately 1 cup)); 1 small green pepper (diced (approximately 1 cup)); 1 can (10.5oz) condensed cream of mushroom soup; 1 can (15 oz) whole kernel corn, drained; 1 cup sour cream; 1/2 teaspoon salt; 1/2 teaspoon pepper; 1 teaspoon garlic powder; 20 oz bag fresh shredded hash browns ((or frozen, thawed)); 3 cups shredded cheddar cheese ((or colby jack or Mexican blend)); 2-3 tablespoons butter, melted ((optional)); chopped green onion ((for garnish, optional))