In a saucepan, combine the soy sauce, water, minced garlic, grated ginger, honey, and brown sugar. Place over medium heat and stir until the sugar has dissolved completely, around 2-3 minutes. In a small bowl, mix the cornstarch with cold water until smooth, then whisk this mixture into the sauce. Continue to cook until it thickens, about 1-2 minutes before removing it from heat to cool.

Take the cooled teriyaki sauce and pour it over the salmon fillets in a dish or bag, ensuring they are well-coated. Cover the dish or seal the bag, then refrigerate for at least 15 minutes to allow the flavors to infuse; for best results, marinate for up to 1 hour.

Preheat your air fryer to 360°F (182°C) for about 5 minutes. Lightly grease your air fryer basket with cooking spray or oil to prevent sticking.

Arrange the marinated salmon fillets in a single layer in the air fryer basket, and air fry at 360°F (182°C) for about 12 minutes, or until the salmon easily flakes with a fork and has a golden color. Brush the salmon with reserved teriyaki sauce during the last 2-3 minutes of cooking.

Carefully remove the salmon from the air fryer using tongs. Transfer the fillets to a serving platter and sprinkle with sesame seeds and sliced scallions. Serve hot, ideally over steamed rice or alongside vegetables.