Preheat oven to 350 degrees. Steam broccoli in microwave for 2 minutes or in a saucepan with water until tender. Drain and set aside. Cut chicken into 2'' chunks. In a skillet bring 1 inch of water to a boil, add chicken and cook just until opaque, about 5 minutes. Drain chicken and pat dry with paper towels. In a bowl combine mushroom soup, mayonnaise, lemon juice, and curry powder. Place broccoli in a buttered casserole dish. Top broccoli with chicken and pour on soup mixture. Top with shredded cheddar cheese and bread crumbs. Dot with bits of butter. Bake for 30 minutes until lightly browned and bubbly