Preheat your oven to 400 degrees.
Note: When cutting the tomatoes up discard the seeds and gel, you only want the tomato.
Cut up the plum tomatoes, mozzarella cheese, and red onion in cubes and place into a small bowl. Cut up two garlic cloves fine and add olive to the bowl. Season with oregano, salt, and pepper. Tear one basil leaf into pieces and add to the bowl. Place in the fridge for about 30 minutes or until you start to see the tomatoes produce a bit of water.
While the tomatoes are setting up in the fridge, peal the other two pieces of garlic and set aside. Cut the baguette into circles, place on a baking sheet and toast in the oven until both sides are a nice golden brown.
Once the bread is brown remove from the oven and while its still hot rub both sides of the bread with the pealed whole garlic. Take the tomatoes out of the fridge and spoon a nice size portion onto each piece of bread, making sure each ingredient is on each piece of bread evenly.
Tear the remaining basil leafs into small pieces and add one or two pieces to each piece of bread. Add a bit of olive oil on top of each piece to ensure it is not dry.