In a small saucepan, combine soy sauce, honey (or brown sugar), mirin, sesame oil, garlic, and ginger.
Heat the mixture over medium heat, stirring frequently until the sugar dissolves.
If you prefer a thicker sauce, mix the cornstarch with 1 tablespoon of water, then add it to the saucepan. Stir until the sauce thickens slightly, about 1–2 minutes. Remove from heat and set aside.
Pat the salmon fillets dry with paper towels to remove excess moisture.
Lightly season the salmon with salt (optional, as the sauce is salty) and a small drizzle of olive oil.
Heat a non-stick skillet over medium heat and add the olive oil.
Place the salmon fillets skin-side down in the pan. Cook for about 4–5 minutes, allowing the skin to crisp up.
Flip the salmon gently using tongs or a spatula, and cook for another 3–4 minutes, or until the salmon is opaque and flakes easily with a fork.
Once the salmon is cooked, pour the prepared teriyaki sauce over the fillets in the pan.
Let the sauce simmer for 1–2 minutes, ensuring the salmon is fully coated and the flavors meld together.
Remove the salmon from the pan and transfer it to a serving plate.
Sprinkle with sesame seeds and green onions for a finishing touch.
Serve immediately with steamed rice, stir-fried vegetables, or a light salad.