Heat oil in a medium saucepan over medium heat. Once hot, add the onions and cook, stirring occasionally, until they have completely softened and begun to brown around the edges. Add the garlic, stir and cook for a minute until fragrant and tanned. Pour in the tomatoes, sprinkle with salt and oregano, stir, cover the pot partially (sauce will want to splatter all over your counters) and simmer for 5 to 6 minutes. Turn off the heat.