Pat the salmon dry with a paper towel and place it into a container skin side up.
In a bowl, combine the soy sauce, rice vinegar, honey, garlic, ginger, sesame oil, and black powder until incorporated.
Save ¼ cup of the marinade for glaze.
Pour the marinade over the fish and make sure it’s thoroughly coated.
Marinade for at least 30 minutes in the fridge.
Make the glaze by combining the leftover marinate and flaxseed powder in a saucepan. Cook over medium heat until it thickens to the consistency of maple syrup, about 5-10 minutes. Picture here shows final consistency.
Preheat the air fryer to 400 °F.
Place the parchment paper in the air fryer tray. Place the salmon, skin-side down, on the parchment, and bake for seven minutes and then add the glaze for the last remaining three minutes.
Test the fish temperature with an internal thermometer. Once it reaches 145 °F, it’s done, and you can remove it.
Sprinkle with sesame seeds and scallions, and serve.