In a large stock pot, bring water to a boil. Add a generous amount of salt and stir. Add penne and cook for 8 to 10 minutes, until al dente. Reserve 2 cups pasta water (don't forget to do this!).
Cook bacon in a large skillet over medium-high heat. Remove slices to a paper towel-lined plate and set aside. Reserve bacon fat in pan.
With bacon fat in pan, add onion and sauté for 5 to 7 minutes, until translucent. Add chili flakes, and stir in tomato paste. Cook for 30 seconds. Add 1 1/2 cups of pasta water and pasta. Stir well until all pasta is coated with the sauce.
Chop bacon and add to pasta. Sprinkle with parmesan and stir until combined. Serve and enjoy.