Fill a pot for the pasta with about 6 quarts of water, place over high heat and bring to a boil.2.
Peel the tomatoes and remove the seeds.
Cut the flesh into ½-inch dice.
Put the olive oil in a 12-inch skillet and place over high heat.
When the oil is hot, add the tomatoes.
Sauté for just 2 to 3 minutes, then season with salt and remove from the heat.
Transfer to the bowl you will be using to serve the pasta.3.
When the water for the pasta is boiling, add about 2 tablespoons salt, add the fusilli and stir well.
Cook until very al dente (about 30 seconds less than you normally would).4.
Coarsely chop enough oregano leaves to measure about 2 teaspoons and add them to the tomatoes in the bowl.
Cut the mozzarella into small ¼-inch dice.5.
When the pasta is done, drain well and toss with the sauce in the bowl.
Add the mozzarella, toss again, then cover the bowl and let stand for about 30 seconds to allow the cheese to melt a bit.
Uncover the bowl, toss one last time and serve at once.