Preheat oven to 350°F. Cook green beans in boiling water in large saucepan 4 to 5 minutes or until tender-crisp. Rinse under cold water; drain well.
Melt butter in same pan on medium heat. Add onions; cook and stir until golden brown, about 5 to 6 minutes. Add mushrooms; cook and stir until tender, about 2 minutes. Add stock, cream cheese, garlic powder, flour and salt; bring to boil. Cook and stir until cream cheese is melted and sauce is thickened and bubbly, about 6 to 7 minutes. Add green beans; toss gently to coat.
Spoon into 2-quart baking dish. Bake 20 minutes. Sprinkle with Crispy Fried Onions. Bake 5 minutes longer or until heated through and top is golden brown.