You'll need some good bread--not that white stuff from the grocery but something with a bit of heft. Get a good, ripe tomato, a jar of mayo, and some green-leaf lettuce...ooh, or some of that Boston lettuce--delicious. Also find some good-quality bacon--thick or thin is up to you.

Heat up a cast-iron pan (really--they're heavy, but hold heat well) on high and place your bacon directly in it without extra oil. You'll probably only get 2-3 pieces in at a time--which is all you need for your sandwich, really. What? You're making one for a friend? That's so lovely of you--but you'll need to do two batches. Watch the bacon cook--it can burn fast. When you've cooked it well on both sides, so it gets that yummy crunchy brown look, take it out with tongs and drain it on paper towels. Once it's cool, layer it on the bread with sliced tomato, lettuce, and mayo-spread bread. 

Voila.