Prepare 1 pound of boneless, skinless chicken breast first. Season the raw chicken with ½ teaspoon garlic powder, ¼ teaspoon salt, and ¼ teaspoon ground black pepper. Cook the chicken (using oil as needed) in a large skillet over medium-high heat until fully cooked. Allow it to cool before cutting it into small pieces. Set aside.
In a small saucepan over medium-low heat, add the 12 ounces of frozen broccoli and allow it to cook until no longer frozen, about 5 minutes. You may also use the microwave for faster results if you prefer.
Preheat the oven to 350 degrees F. In a medium-sized bowl, stir together the 1 can (10.5 ounces) of cream of chicken soup and 3 tablespoons of mayonnaise until combined. Add the prepared chicken to the soup mixture and stir to combine.
Grab a 9x13-inch rectangle baking dish and lightly spray with cooking spray before spreading the chicken mixture at the bottom in an even layer.
Top the chicken mixture with the prepared broccoli and spread in an even layer.
Add the 1 ½ cups of shredded cheddar cheese on top in an even layer and place into the oven to bake for about 20 to 25 minutes or until the cheese has completely melted and is bubbly and lightly golden.
Carefully remove the chicken casserole from the oven and serve warm with cooked rice or egg noodles. Enjoy!