Cut the cantaloupe half into thirds; cover and chill two of the wedges. Peel and dice remaining wedge; set aside.
Cook macaroni shells according to package directions. Drain and rinse with cold water. Drain again; set aside.
In a small bowl, combine diced cantaloupe, chicken, honeydew, yogurt, lemon juice, chives, and mustard. Spoon about 1/4 cup of the mixture into each pasta shell. Arrange two filled shells and a chilled cantaloupe wedge on each of two serving dishes. If desired, garnish with thyme sprigs.