Preheat oven to 350°F and grease a 9x13-inch baking dish.
Make the sauce: In a mixing bowl, whisk together cream of chicken soup, mayo, sour cream, garlic powder, salt, and pepper until smooth.
Layer the dish: Spread broccoli evenly in the dish, then top with chicken.
Add the sauce: Pour and spread the creamy sauce mixture over the chicken and broccoli.
Top with cheese: Sprinkle shredded cheddar cheese evenly over the top.
Make the topping: In a small bowl, mix crushed crackers with melted butter and sprinkle on top.
Bake for 25–30 minutes until bubbly and golden brown.
Rest for 5–10 minutes before serving for best texture.