Place the chicken breasts in a large pot and cover them with water. Bring to a simmer and cook until the chicken is cooked through - 15 to 20 minutes. Be cautious not to boil the chicken as it has a tendency to get tough when boiled. Remove from water to allow to cool. Once cooled, shred chicken.
Preheat oven to 350°F and spray a 9x13-inch baking dish with nonstick cooking spray.
In a large bowl, combine the sour cream, mushroom soup, garlic, and salt and pepper to taste. Mix well. Add about half of the poppy seeds and the chicken to the bowl and mix well. Pour the mixture into the prepared dish.
In a medium bowl, combine the melted butter, crushed crackers, and the remaining poppy seeds. Mix well and sprinkle over the chicken mixture. Bake for 20 to 30 minutes or until bubbly and heated through. Serve over white rice, if desired.