Heat the olive oil in a large pot over medium heat.
Add the diced onion and cook for about 5 minutes, until it softens and turns translucent.
Stir in the minced garlic and cook for about 1 minute, stirring gently so it does not burn.
Pour in the crushed tomatoes and stir everything together.
Add the oregano, basil, salt, pepper, and sugar if using.
Bring the sauce to a gentle simmer.
Lower the heat and let the sauce simmer for about 30 minutes, stirring occasionally.
If the sauce gets too thick, add a small amount of water until it reaches the texture you like.
Taste and adjust seasoning as needed.
Serve over freshly cooked spaghetti or spoon it on top and enjoy.