Preheat oven to to 350 degrees F.
In a 13 x 9 x 3 inch baking dish, arrange broccoli spears in 2 rows with stalks facing toward the center. Spoon chicken on top of the stalks, and top chicken with cheese. Set aside.
In a heavy saucepan, combine milk, lemon juice, curry powder, pepper, and cream of mushroom soup. In a small bowl, combine flour and water until combined. Add to soup mixture. Bring to a boil over medium heat, stirring constantly with a whisk. Cook until thickened, stirring constantly. Pour over chicken.
In a small bowl, combine Melba toast crumbs and butter. Sprinkle over soup mixture. Cover and bake at 350 degrees F for 2o minutes. Uncover and bake an additional 15 minutes. Let stand 10 minutes.