Whisk together the tamari, rice vinegar and coconut sugar until the sugar dissolves. Pop the mixture into a shallow dish, coat both sides of the salmon with the mixture, and then arrange the salmon skin side up in the dish. Pop into the fridge for at least 30 minutes
After 30 mins, move the racks in the broiler as close to where the flame will be, as you can (making sure your skillet can still fit in there). Turn the broiler to high
Put the stove on high heat. Place the cast iron skillet on the heat and allow it to get VERY hot (if you do not have a well seasoned pan, you will need to add a little bit of cooking oil here - I would suggest avocado oil)
Turn the stove off. Add the salmon, skin side up to the hot skillet, and pop into the broiler (be careful - the pan is very hot here)
Cook for 1-2 minutes in the broiler. If it is a thicker cut, you may have to flip, and cook for another 1 minute.
Serve and enjoy