Simmer chicken breasts in water, celery, and onion for one hour. Remove chicken and cut or shred into pieces. Butter and line baking pan with broccoli. Put chicken on top of broccoli. In a bowl, mix mayonnaise, cream of chicken soup, curry powder, and lemon juice. Add mixture on top of chicken and broccoli. Top with shredded cheddar cheese. Bake at 350 for 45 minutes.