We are all familiar with japanese condimentssuch as soy sauce or tonkatsu saucewhich instantly add flavor to fish or protein that's been simply cooked with salt and pepper. But if you enjoy onions, try this recipe for japanese spicy onion sauce and you won't be disappointed. It's savorywith a soy sauce (shoyu) base and sweet onionsbut its flavor is more complex with the addition of oyster sauce and chili garlic paste. What makes this sauce appealing is that it's quite quick and easy to make, particularly because it uses oyster sauce and chili garlic paste, both of which are bottled and available for purchase at japanese or other asian grocery stores. Both of these sauces are worth adding to your list of essential ingredients to keep in the refrigerator. The soy sauce and sugar are added last so that the soy sauce does not reduce and become salty. Depending on your preference, add more or less sugar to create a savory-sweet sauce. Only a small amount of the sauce is needed to season your seafood or protein. The onion sauce may be kept in the refrigerator for up to five days or stored in the freezer in small ice cube portions for future use.