Pa amb tomàquet, bread with tomato. No, really.

You take some slices of bread, or something like a baguette or ciabatta sliced longitudinally to make a sandwich. Good bread, mind, not that spongy stuff you get in the U.S. Something with some crust, with a bit of a crunch. Slightly toasted (but not burnt) is good, and easier, but not necessary. You can eat this hot or cold, it's good either way.

Anyway, as I was saying you take some bread, and you take some tomatoes. Red, juicy, the tastiest the better. Slice one in half, take half, rub the sliced part on one side of the bread (on the crumb, obviously, not the crust), until the bread has soaked a good amount of the tomato's juice (you could do both sides if you wanted to, but it'd probably be a bit of a mess). It's not a problem if some small bits of the tomato's meat also end up in the bread, but you don't want big chunks (unless you want tomato as a topping, though that'd be a bit redundant). You don't want the bread to get too soft, don't ruin that crunch. If the tomato is juicy enough you can reuse it for the next slice, until it runs out of juice or you're just left with the skin.

Once you've got all your slices done, sprinkle some salt over them. Don't go overboard, you want to be able to taste the bread, and the tomato.

Finally, dribble some good virgin olive oil on them. Again, don't go overboard, don't drown them. Once you're done you can take one of the slices and use it to help spread the oil and salt on the other ones by tapping the crumbs against each other.

You can now eat the slices as they are, toast them if you want, accompany them with cured meats (cured ham is fantastic with this) or cheeses, as a side or as toppings, or as the filling of a sandwich (seriously, unless you're making a hot dog, or a cheese melt, or a hamburger, or something like that this is the way to make a sandwich; once you've tried it you won't be going back to plain or buttered bread).

Experiment, have fun, try different kinds of bread, more or less tomato, oil, or salt, toasted or untoasted, different toppings (anything you'd put in a sandwich will almost certainly work), oil from different types of olives, maybe rub some garlic on the bread before the tomato, if it's hard enough to take it... there are infinite possibilities and combinations, and unless you go overboard with the toppings they're just five minutes away as long as you've got some bread, some tomatoes, some olive oil, and some salt.

(Also, if you've got really good bread and really good oil, but would rather skip the tomatoes, pa amb oli, bread with oil — and a sprinkle of salt — can also be an excellent snack to eat by itself before a meal, though pa amb tomàquet is better if you want to eat it with toppings, or as a sandwich.)