Mix together chopped turkey, mayonnaise, relish, celery and onion.
On a baking sheet lay your 6 slices of toast. Spread the turkey mixture evenly on the 6 slices of toast. Cover with a slice of cheese.
Turn on your oven's broiler and move one of your oven racks to the highest possible setting.
When the broiler is heated, slide your turkey melts onto the highest shelf. Close the oven door part way, leaving it open the final couple of inches (I frequently use a pot holder to wedge the door open).
Keep an eye on the sandwiches as the cheese melts and the top bubbles. It will only take a few minutes and can go from done to burnt very quickly.
Remove from the oven and serve!