Start by making glaze for salmon. In a small sauce pan, add in soy sauce, miso paste, orange juice and zest, sugar, water, and chopped fresh ginger. Cook on medium heat for 5-10 minutes, or until reduced to just coat the back of a spoon.
While glaze is reducing, pat down salmon with a clean paper towel. Season with salt. Set aside.
Heat a cast iron skillet on high. When you see smoke start to come off the pan, reduce the heat to medium high. Then add oil and let sit for a few seconds. Once oil is glistening and hot, add in salmon. If there is skin on the salmon, place down the salmon skin side down first. Allow to sear and do not move from pan for 3-4 minutes.
After 2-3 minutes, or when a golden brown crust forms on the salmon skin and it feels crispy, gently turn over and allow to sear for another 3-4 minutes on the other side.
Check on the glaze to prevent burning. It is done when it gently coats the back of a spoon. Adjust for seasoning.
Remove salmon from cast iron skillet when both sides have a golden brown sear. Top with orange miso glaze.