Heat olive oil in a large saucepan over medium heat.
Add chopped onions and sauté until translucent, about 5 minutes.
Stir in the minced garlic and cook for another 1-2 minutes.
Pour in the crushed tomatoes and add the tomato paste.
Season with oregano, basil, salt, and pepper.
Bring the mixture to a simmer, stirring occasionally.
Reduce heat and let the sauce simmer for 20-25 minutes until thickened.
Taste and adjust seasoning if necessary.
Remove from heat and let it cool slightly.
Serve over cooked spaghetti, garnished with fresh parsley.