Bring 1/2 cup of water to a boil in a large skillet on medium high heat. Add the sliced onions and spread them out in the pan.

Turn them a few times until they are softened and the water has almost evaporated.

Spoon the olive oil over the onions and add the garlic and 1/2 teaspoon salt.

Stir the onions and continue cooking until they are light golden and soft.

Push the onions to one side of the pan and add the diced pancetta.

Cook until the pancetta has become brown and crispy.

Stir the onions and pancetta together with the hot pepper flakes.

Add the tomatoes with their juice, stir, bring to a boil and simmer for about 15 minutes or until slightly thickened.

Meanwhile, bring a large pot of water to a boil and add 1 tablespoon of kosher salt.

Add the pasta to the boiling water all at once and cover the pot to bring the water back to a boil.

Uncover and cook until the spaghetti is almost al dente. Bring the sauce back to a boil and add the spaghetti to the sauce along with some of the pasta water.

Stir to coat the pasta and serve in shallow bowls with freshly grated Parmesan.