Preheat the Oven – Set your oven to 375°F (190°C) and grease a 9x13-inch baking dish.
Cook the Chicken – Heat olive oil in a large skillet over medium heat. Add the cubed chicken, season with salt and ¼ teaspoon black pepper, and cook for about 5 minutes until lightly browned. Remove from heat.
Prepare the Creamy Mixture – In a large mixing bowl, combine the cream of chicken soup, mayonnaise, sour cream, cheddar cheese, milk, lemon juice, garlic powder, onion powder, and the remaining ¼ teaspoon black pepper. Stir until well mixed.
Assemble the Casserole – Spread the thawed broccoli evenly in the greased baking dish. Layer the cooked chicken on top, then pour the creamy mixture over everything, spreading it evenly.
Make the Crispy Topping – In a small bowl, mix the breadcrumbs with melted butter. Sprinkle the breadcrumb mixture evenly over the casserole.
Bake Until Golden – Bake uncovered for 30-35 minutes, until the casserole is bubbly and the topping is golden brown.
Serve & Enjoy – Let the casserole rest for a few minutes before serving. Pair with rice, a side salad, or garlic bread for a complete meal.