In a large skillet, heat oil over medium-high heat. Toast rigatoni in the skillet until golden brown, about 3 minutes. Add in the garlic, onion and pepper flakes, and cook until tender, about 2 minutes. Mix in tomato sauce and 2 cans water. Cook until pasta is tender, about 8-10 minutes.
Once pasta is done, stir in cheese and let melt, about 1 minute.
Scoop into bowls and garnish with cilantro.