In a saucepan over medium heat, melt spread. Add mushrooms and onion; cook for 10 minutes, stirring frequently. Stir in flour; cook for an additional 5 minutes. Gradually pour in stock, bring to a boil, then reduce heat and simmer for 10 minutes. Add half & half and season with salt and pepper. Set aside.
Preheat the oven to 350 degrees F. Boil the beans for 5 minutes, then drain. Combine with mushroom sauce and transfer to a 11 x 7-inch baking dish.
Mix all topping ingredients until thoroughly combined, then sprinkle along the edges of the beans.
Bake until the top is beautifully golden for about 20 minutes.