Probably bacon, but I love fried bologna too.
What you need is thick cut applewood bacon. Fry it up, not too crispy. A home grown, red ripe tomato. NOT a grocery store tomato. If you don't know the difference, I feel great pity for you. Toast your bread lightly, spread Hellman's mayo on both sides. Squirt some Heinz mustard on the slice your bacon will lay on. Place your cooked bacon on this slice. Next, a slice of sharp cheddar cheese. Having peeled and sliced your home grown, red ride tomato in slices about a quarter inch think, place two slices on your cheese. Sprinkle some black pepper on the other slice of bread and make your sandwich. Experience Heaven.