Preheat oven to 350°F. Spray a 9x9-inch baking dish with cooking spray.

If your chicken is not already cooked: place the 4 chicken breast halves in a saucepan and add enough water to cover. Simmer 20–30 minutes, until cooked through (internal temperature 165°F). Remove, drain, let cool slightly, then cut or shred into bite-size pieces (about 2–3 cups cooked).

Cook the 1 1/2 pounds broccoli florets until tender-crisp (steam or blanch), then drain.

Spread the cooked broccoli evenly in the bottom of the prepared baking dish.

Arrange the cooked chicken pieces evenly on top of the broccoli.

In a medium bowl, stir together the 10.5-oz can cream of chicken soup, 1/2 cup milk, 1/4 cup mayonnaise, 1/4 cup salad dressing, 1 cup grated cheddar cheese, and 1 teaspoon lemon juice until well blended.

Spread this soup-and-cheese mixture evenly over the chicken.

Sprinkle 1/2 cup bread crumbs and 1/4 cup grated Parmesan cheese over the top, then dot evenly with the 2 tablespoons butter (cut into small pieces).

Bake in the preheated 350°F oven for 30 minutes, until heated through and the topping is lightly browned. Let rest a few minutes before serving.