Dissolve the Gateway seasoning in the soy sauce. Smear the mustard on the flesh side of the filets. Heat the oil in a saute pan until almost smoking. Place the filets mustard side down, and sear until golden brown. Flip the salmon, reduce heat and cover. Let cook about 3-4 minutes. Remove the lid, increase the heat and pour in the soy mixture. As the salmon finishes, the soy and maple will cook down to leave a nice glaze.
If you prefer a more rare piece of salmon, don't cover the pan while cooking, just let it saute evenly on both sides.