Heat the oven to 350°F and butter a 3-quart baking dish with 1 teaspoon of the melted butter.
Stir the chicken, soup, sour cream, lemon juice, poppy seeds, garlic powder and pepper together in a large bowl.
Spread the chicken mixture evenly in the prepared dish.
Toss the cracker crumbs with the remaining melted butter until every piece is lightly coated.
Scatter the crackers over the filling without pressing them down.
Bake for 30 to 35 minutes, until the edges bubble, the top is browned and the center reaches 165°F, then rest for 5 minutes.