Combine the first three ingredients in a medium saucepan and bring to a boil. Reduce the heat and let simmer for about 20 minutes until the liquid reduces by half and becomes syrupy. Pour into a bowl and set aside to cool.

Pour the sesame seeds onto a large plate or pan. Pat the salmon dry and sea- son with salt. Take one salmon filet at a time, and spread each side with about a tablespoon of mustard. Then press it into the sesame seeds to evenly coat each side. Set aside and repeat with the remaining fish.

Heat the oil in a large cast iron or nonstick skillet, about medium-high heat. When the oil is shimmering and hot, carefully place each filet in the pan. It’s important not to overcrowd the pan, so if it doesn’t look like they will all comfortably fit, do it in batches. Cook for about 2 minutes, then carefully flip it over to the other side. Cook for one more minute (two if you prefer it well done) and remove from the pan.

Drizzle with the sweet soy glaze and sprinkle with scallions. Serve with steamed baby bok choy and rice if desired.