Heat the oven to 350°F and butter a 9-by-13-inch baking dish with 1 teaspoon of the melted butter.
Arrange the broccoli in an even layer and spread the cooked chicken over it.
Whisk the soup, mayonnaise, lemon juice, curry powder, salt and pepper until smooth, then spoon it over the chicken.
Sprinkle the cheddar evenly over the sauce.
Mix the bread crumbs with the remaining melted butter and spread them over the cheese.
Bake for 30 to 35 minutes, until browned, bubbling in the center and 165°F in the thickest part, then rest for 5 minutes.