Heat the oil over medium heat, add the onions, garlic and fry on a medium heat for 5 minutes till translucent
Add the tomatoes, bring to boil and then simmer on medium-low heat for 15 minutes.
Add the spices, season and simmer for 5-10minutes longer to get a thick sauce (the sauce has right consistency when after you run a spatula against the bottom of the frying pan, the sauce stays in its place).
Notes
You can keep it in a jar in a fridge for up to 4 days or you can freeze it.