Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the cooked, shredded chicken, cream of chicken soup, sour cream, garlic powder, onion powder, black pepper, and salt. Mix until well combined.
Spread the chicken mixture evenly in a greased 9x13-inch baking dish.
In a separate bowl, combine the crushed crackers and melted butter. Mix until the crackers are evenly coated.
Sprinkle the cracker mixture evenly over the chicken layer in the baking dish.
Top with shredded cheddar cheese.
Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the top is golden brown.
Remove from the oven and let it cool for a few minutes before serving. Garnish with chopped green onions if desired.