Most of the sauces you buy have a lot of sugar added to them.
I make my own, albeit not as 'saucy' but just as tasty, with soy sauce, chilli, garlic and a little of the noodle or rice cooking water.
It's amazing if you add pineapple to it too, although you'd need to add about 0.5 syn to a serving as the fruit gets a syn value when cooked.
The sauce comes out like a spicy chow mein style flavour.