Slice the potatoes so that you have medium sized circles.
Slice the onions into pieces or rings, your choice on the size.
On a large piece of foil, spray the bottom with a non-stick vegetable spray and lay down some onions.
Then lay down a row of the potato circles and another layer of onions. Keep rotating until you're halfway done and place 3 pieces of each cheese, laying the flavors every-other style(1 american, 1 cheddar, 1 american..you get the idea).
Add more of the alternating rows of onions and potatoes. But before you run out of potatoes, throw in the last 6 slices of cheese. (Don't put on top because the cheese will stick to the foil if you flip it!)
Spray on another coat of the non-stick vegetable spray and seal up the foil. (I usually throw on another layer of foil once it is closed up.)
Throw it on the grill or in the stove, and flip every so often until done. (about 20-25 minutes heat time)