In a small bowl mix the Teriyaki sauce, soy sauce, mirin, ginger and garlic pour all but 4 tbsp of the marinade over salmon and let it marinade for 30 minutes in the refrigerator. Keep the reserved marinade for the bok choy.
Preheat the oven to 350F/180C.
Take the salmon fillet out of the marinade and arrange on a baking sheet together with bok choy. Brush the teriyaki marinade over bok choy and bake in the oven for 20 minutes.
While the salmon and the bok choy are cooking, put the marinade in a small saucepan and bring to a boil. Set aside
Take the salmon and bok choy out of the oven, remove the bok choy to a serving plate. Change the oven setting to a broil/grill and move the oven rack closer to the element, then broil the salmon for 1-2 minutes for a caramelised top, watch closely!
Take the salmon out of the oven and brush additional marinade over the salmon and bok choy, sprinkle with sliced spring onions and sesame seeds.
Serve immediately with rice, noodles or on it's own for a low carb dinner.