My mother-in-law made these for me one time, and I love them! I have recently made them for my family, and they love them too! There are a couple of different ways you can make these, so try different ways, and let me know how you like them!
Take a slice of bread, put a light layer of mayo on it, sprinkle with salt and pepper to taste.
Put cheese on top of the mayo, and finally top with one slice of tomato.
*Variation* Put tomato on top of mayo, and put cheese on top of that. (We do ours this way, but my mother-in-law does it the other way.)
Put on cookie sheet lined with foil (for easy clean up), and put in the oven. It may take 10-15 minutes to cook these, depending on how close you have your rack, and how many you put in there. Watch closely, and when the cheese is melted with a little bit of brown bubbles, they're done!
Enjoy as an appetizer, side with some chicken, or as your main course!