The onion oil mentioned in the video is made by frying onions slices in oil until the onion is brown and slightly crispy.

You can prepare this in bulk and store untill you need to use it. It keeps well in the refrigerator if you prepare a lot of it.

Using onion oil instead of plain oil adds fragrance to food. For those who try Asian cooking at home, this may be reason why what you cook lack a little oomph compared with what you eat in restaurants. Restaurants will prepare onion oil in bulk and use a little of it in their cooking.

The fried onion that was sprinkled is from the preparation of onion oil. It serves as a garnishing as well as adds a slightly sweet and fragrant taste.

If you like the bitter gourd soft instead of crunchy, you can stir fry it before adding the other ingredients.

In order to save time, what restaurants do is blanche the bittergourd instead of  washing it with salt and squeezing to reduce bitterness. The length of time it is kept in the boiling water depends on how soft/crunchy you want the bittergourd to be.