Halve the tomatoes lengthwise through the stems. Squeeze the tomatoes over a bowl or sink to remove the seeds and watery centers. Chop the remaining tomato flesh roughly and transfer to a food processor. Add the oil, tomato paste, sugar, oregano, garlic, 1 tablespoon salt and some pepper and pulse until mostly pureed with some small chunks. Pour into a fine-mesh sieve over a bowl and let some of the watery liquid drain, shaking gently for about 30 seconds to help it out. Pour the tomato sauce into another bowl or jar and use immediately or refrigerate up to 1 day.