Preheat the oven to 350°F (175°C).

Dice 3 cups of cooked chicken and chop 1/2 cup diced celery, 1/2 cup diced red onion, and 1/4 cup fresh parsley.

In a large mixing bowl, combine 1 cup mayonnaise, 1 teaspoon salt, 1/2 teaspoon black pepper, and 1/2 teaspoon garlic powder, stirring until smooth.

Add the chicken, celery, red onion, and parsley to the mayo mixture and fold gently until everything is coated.

Fold in 1/2 cup slivered almonds or chopped pecans and 3/4 cup shredded cheddar cheese.

Crumble 4 slices of cooked bacon into the mixture and fold in gently.

Transfer the mixture to a 9x13-inch baking dish, spreading it into an even layer.

In a small bowl, mix 1/2 cup panko breadcrumbs, 2 tablespoons melted butter, and the reserved 1/4 cup shredded cheddar cheese until the crumbs are evenly coated.

Sprinkle the breadcrumb mixture evenly over the chicken salad layer, pressing lightly to adhere.

Bake in the preheated oven for 25 minutes, or until the top is golden brown and the edges are bubbling.

Remove from the oven and let the dish rest for 5 minutes before serving.