Once the Macaroni & Cheese is prepared, set it aside.
Spread a small amount of butter on each slice of bread, then place about 1 cup of the Macaroni & Cheese on one slice of bread. Be sure to place this on the not-buttered side.
Top it with about 1/2 cup of the shredded chicken. Place the other slice of bread on top of the shredded chicken, buttered side up.
Place the sandwich on a greased grill pan, lightly grill it on each side.