1. Preheat the oven to 350°F (175°C).
2. In a large bowl, combine the shredded chicken, steamed broccoli, and cheddar cheese.
3. In a separate bowl, mix the mayonnaise, sour cream, Parmesan cheese, lemon juice, curry powder, salt, and pepper until well combined.
4. Pour the mayonnaise mixture over the chicken and broccoli mixture, stirring gently to coat everything evenly.
5. Transfer the mixture into a greased 9×13 inch baking dish, spreading it out evenly.
6. In a small bowl, mix the panko breadcrumbs with the melted butter until the crumbs are moistened.
7. Sprinkle the buttered breadcrumbs evenly over the top of the casserole.
8. Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and the casserole is bubbling.
9. Let it cool for a few minutes before serving.
