Cook and drain pasta as directed on package. Rinse with cold water; drain.
In large bowl, mix pasta, chicken, grapes and onions. In small bowl, mix mayonnaise, milk, mustard and salt; stir into pasta mixture.
To serve, place 3 watermelon wedges on each of 6 dinner plates. Divide salad evenly among watermelon wedges. Sprinkle with almonds.