Heat olive oil in a medium saucepan over medium heat.
Add the diced onion and red pepper flakes, and sauté until the onion is soft and translucent.
Add the minced garlic and cook for about 1 minute more, until fragrant.
Stir in the tomato paste, diced tomatoes, tomato sauce, and oregano.
Bring the sauce to a boil, then reduce the heat to low and let it simmer for about 20 minutes, stirring occasionally.
Using a handheld immersion blender or a stand blender, carefully blend the sauce to your desired smoothness.
Season with salt and pepper to taste before serving.
Add a handful of fresh basil leaves at the very end of cooking for a burst of fresh, aromatic flavor.