Preheat the oven to 350°F.
Lightly grease a 9x13 pan, and put the cooked chicken evenly in it.
In a medium bowl, stir together the sour cream, soup, Worcestershire sauce, salt, garlic powder, and pepper.
Spread the soup mixture all over the chicken.
Put the crackers in a plastic zipper bag, and smash them into chunky crumbs.
Mix the melted butter with the cracker crumbs. I do this right in the plastic bag.
Sprinkle the buttery crackers on top of the saucy chicken.
Sprinkle the poppy seeds on top of the cracker layer.
Bake for 20 to 30 minutes, until the crackers look toasty.