Combine ingredients in pan and bring to a boil: Combine pasta, tomatoes, onion, garlic, red-pepper flakes, basil, oil, 2 teaspoons salt, ¼ teaspoon pepper, and water in a large straight-sided skillet. Bring to a boil over high heat.
Cook, stirring: Boil mixture, stirring and turning pasta frequently with tongs, until pasta is al dente and water has nearly evaporated, about 9 minutes.
Season and serve: Season to taste with salt and pepper, divide among 4 bowls, and garnish with basil. Serve with oil and Parmesan.
