Preheat oven to 375*F (190*C). In a small saucepan over medium heat, melt butter. Add flour, salt and pepper, stirring constantly, until bubbly. Stir in milk. Heat to boiling, stirring or whisking constantly until thickened, about 1 minute. Add green onions. Makes about 1 cup. In a lightly greased 2 1/2-quart casserole dish, mix all ingredients together. Season with salt and pepper to taste. Sprinkle bread crumbs on top. Bake uncovered, until hot, about 25 minutes. Serves 4. Note: For a thin white sauce, decrease butter and flour to 1 tablespoon each. For a thick white sauce, increase butter to 4 tablespoons and flour to 1/4 cup.