You're wondering how I make it? Here ya go, complete with pictures:
In a bowl I mix tomato, onion, basil (fresh when I have it) and olive oil.
While the flavors are mingling, I toast the bread. I like to put a little olive oil on the bread and then let the oven do the work.
Once the bread is toasted, I top the bread with the tomato mixture and if I have it I like to top it with cheese.
Then I put it back in the oven till the cheese is melted. Once you take it out, Enjoy!