Place salmon skin side down on a lightly greased baking sheet.
In a small bowl whisk together mustard, soy sauce, sesame oil, and garlic until smooth, then drizzle half the mixture over the salmon.
Allow the mixture to sit 10 minutes and then bake for 15-20 minutes. Allow the fish to cool a few minutes and then drizzle or brush with the remaining glaze.
Top with toasted sesame seeds and green onions. Serve with steamed rice if desired.