In a large, straight-sided skillet, place your pasta in the middle so it lies flat.
Add the tomatoes, onion, garlic, spinach, oil, red pepper flakes (if using), 2 teaspoons of salt, and 1/4 teaspoon of pepper distributing evenly around the pan.
Add the water.
Bring to a boil over high heat, then reduce to medium high.
Boil pasta mixture, uncovered, stirring and turning the pasta frequently with tongs or a fork to separate.
Cook until pasta is al dente and water has almost evaporated, 8-10 minutes.
Divide among four shallow bowls, drizzle with olive oil, and sprinkle with salt, cracked pepper and some Parmesan if desired.