Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the shredded chicken, sour cream, cream of chicken soup, garlic powder, onion powder, black pepper, and salt. Mix well until all ingredients are fully incorporated.
Fold in 3/4 cup of the shredded cheddar cheese and the chopped green onions, if using.
Transfer the chicken mixture into a greased 9x13-inch baking dish, spreading it evenly.
In a separate bowl, combine the crushed crackers with the melted butter. Mix until the crackers are well coated.
Sprinkle the cracker mixture evenly over the chicken mixture in the baking dish.
Top with the remaining 1/4 cup of shredded cheddar cheese.
Bake in the preheated oven for 30-35 minutes, or until the casserole is bubbly and the top is golden brown.
Remove from the oven and let it cool for about 5 minutes before serving.