Cut squid along the body tube, then grasp the head and pull away from the body. Remove the cartilage in the body and peel the skin membrane away.
Cut the tentacles from the head just below the eyes. Discard the innards, head and beak, reserve the tentacles.
Lay the squid body flat on a cutting board with the inside surface facing you. Use a sharp knife to score diagonal cuts in a crisscross pattern, about ½-¾ inch apart, on the inside surface. Do not cut all the way through. You can watch the video in the post to see how to clean and cut the squid.
After scoring, slice the squid body into smaller pieces. Also slice the tentacles into smaller pieces if needed. Mix the squid with salt, pepper and sesame oil and set aside for 5-10 minutes.
Slice scallion stalks into 2-inch long pieces. Cut ginger into thin slices and then julienne. Also cut chili into thin slices.
Arrange two thirds of the scallion and ginger in a large heat-proof shallow plate or bowl that can fit inside your steamer. Then pile the squid pieces on the aromatics. Scatter the remaining scallion, ginger and chili on top.
If using a bamboo steamer, no need to cover the plate. If not, cover the plate with foil. Steam for about 6-8 minutes or until the squid is just cooked through. Check the doneness after 5 minutes to avoid overcooking which will make the texture become rubbery.
Serve immediately with fish sauce on the side. You can also sprinkle more salt and pepper over the steamed squid.
I recommend using squids of small size for the best taste and texture. You can also cut the squids into rings, which is easier. Scoring then slicing will make it look prettier though.