Place the onions in a bowl and add a couple of teaspoons of water- I also like to add a boullion cube for extra flavor (+5 calories), but be careful with this if you're watching sodium.
Cover with plastic wrap and nuke onions for about 3-5 minutes or until floppy.
Meanwhile, spray one side of each slice of bread with the butter spray.
Lay one piece spray-side down in a skillet and top with the cheese.
You might want to add a squirt of spray over the cheese if the kind you use doesn't melt well.
When the onions are done, take them out and spoon them over the cheese on the bread.
Next, add the 3 slices of turkey.
Spread the unsprayed side of the other slice of bread with the Miracle Whip (or fat free mayo) and the mustard.
Place this slice on top- spray side up!
Heat the skillet over medium heat, toasting the sandwich a couple of minutes on either side or until golden brown.
When done, remove the sandwich, peel apart, stuff in the lettuce, smoosh back together, and CHOW DOWN!
I included calorie and fat counts for every ingredient so that it will be easy to make substitutions and still know the exact nutritional information- I realize that not everyone loves onions as much as I do!
Some other good ingredients are roasted bell peppers, mushrooms, tomato, or anything else you love!