Make the glaze. In a small bowl, whisk together the olive oil, miso paste, coconut aminos, rice vinegar, honey if using, garlic, ginger, mustard, and 1 tablespoon water until smooth. Add a little more water if needed to make the glaze easy to brush onto the salmon. Set aside about one third of the glaze for later.
Prepare the salmon. Pat the salmon steaks dry with paper towels. Lightly brush both sides with olive oil, season with sea salt and black pepper. Brush the remaining glaze over both sides of the salmon.
Sear the salmon. Heat a cast iron skillet over medium heat. Lightly oil the skillet if needed. Add the salmon and cook for 3 to 4 minutes, until nicely browned and crispy. Carefully flip and cook for another 3 to 4 minutes, depending on the thickness.
Add the remaining glaze. During the last minute of cooking, brush the salmon with the reserved glaze.
Finish if needed. If your salmon steaks are very thick and need more time, transfer the skillet to a 400°F oven for another 3 to 5 minutes, or until cooked to your liking.
