In a small bowl, sprinkle gelatin over cold water; let stand for 1 minute. In a saucepan, heat milk over medium heat until bubbles form around sides of saucepan. Add gelatin mixture; stir until dissolved. Stir in brown sugar until dissolved. Remove from the heat. Add the pumpkin, ginger, cinnamon and salt; mix well. Refrigerate until thickened, about 1-1/2 hours.
Fold whipped topping into pumpkin mixture. Pour into crust. Refrigerate for at least 4 hours or until firm. Refrigerate leftovers.