Heat olive oil in a large saucepan over medium heat. Add the chopped onion and sauté for 3-4 minutes until softened.

Stir in the minced garlic and cook for another 30 seconds until fragrant.

Add the crushed tomatoes, diced tomatoes, and tomato paste. Stir to combine.

Season with salt, black pepper, oregano, basil, and red pepper flakes. Stir well.

Bring the sauce to a gentle simmer, then reduce the heat to low. Let it simmer uncovered for 25-30 minutes, stirring occasionally.

If the sauce is too acidic, add a teaspoon of sugar to balance the flavors.

Remove from heat and stir in fresh parsley or basil. Adjust seasoning if needed.

Serve warm over pasta, pizza, or as a dipping sauce for breadsticks.