Bring a pot of water to boil. Add the tomatoes and cook for 90 seconds. Remove with a slotted spoon and place immediately into a bowl of ice water to stop them from cooking. Peel the tomatoes, cut them in half, remove the seeds, and julienne into ½-inch strips. If using canned tomatoes, add to a bowl and mash them together with your hands.
Bring another large pot of salted water to a boil.
In a large skillet, over medium heat sauté the garlic in the olive oil until it turns golden. Add the tomatoes, salt and pepper. Cook over medium heat for about 10 minutes, or until the tomatoes release their juices and begin to reduce slightly. Add the basil and cook for about 5 minutes more.
Cook the spaghetti until al dente (about 2 minutes less than package directions), drain, and add it to the tomatoes. Cook together for about one minute.
Serve garnished with basil leaves and grated Parmigiano.