Start boiling salt water for spaghetti.
Place in a large skillet the oil and parsley, over medium heat.A couple of minutes later add garlic (remove it when light brown).
When the oil is hot, add tomatoes and oregano. Crush the larger tomato pieces.
A couple minutes before spaghetti are cooked, add mozzarella..
When the water boils, add spaghetti and cook for 9 minutes. Drain well.
Place drained spaghetti in the skillet, over medium heat, and mix well for a minute or two.
Serve immediately, with grated cheese or not, to taste.