Step 1: Prep. Heat the oven to 350 degrees F and grease a 7x11 inch or 9x9 inch baking dish.
Step 2: Mix the filling. In a large bowl, stir together the chicken, soup, sour cream, 2 teaspoons poppy seeds, garlic powder, onion powder, and pepper until evenly coated. Add a splash of broth if it feels stiff.
Step 3: Spread. Spread the mixture into the baking dish in an even layer.
Step 4: Make the topping. Mix the crushed crackers, melted butter, and 1 tablespoon poppy seeds until the crumbs are evenly coated. Sprinkle over the chicken.
Step 5: Bake. Bake for 25 to 30 minutes, until the sauce is bubbling around the edges, the topping is golden brown, and the casserole is hot in the center (165°F / 74°C).
Step 6: Rest and serve. Rest for 5 minutes, then serve over egg noodles or rice.