Heat the broiler by placing the oven rack 6 inches from the element. 5 minutes over medium heat in a 12-inch cast-iron skillet Toss tomatoes with 1 teaspoon salt and oil.
Cook, stirring periodically, until tomatoes are gently browned and blistered, about 10 minutes. Cook for 30 seconds after adding the garlic, tomato paste, and pepper flakes. Using a potato masher, roughly mash tomatoes off the heat.
Bring the water and pasta to a boil over medium-high heat. Reduce heat to a vigorous simmer, cover, and cook, tossing frequently, for 15 to 18 minutes, or until pasta is tender.
Stir in the Parmesan and, if necessary, add more hot water to thin down the sauce. Season with salt and pepper to taste after adding the basil. Lastly, top with mozzarella.
Transfer skillet to oven and broil for 5 minutes, or until cheese is melted and spotty brown. Serve.
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.