Prepare the teriyaki sauce by whisking together soy sauce, mirin or honey, grated garlic, and grated ginger in a small bowl. If using cornstarch, mix it with a little water and add to the sauce to thicken it.
Pat the salmon fillets dry and brush them evenly with half of the teriyaki sauce. Let them marinate for 15-30 minutes at room temperature to absorb flavors without becoming overly salty or mushy.
Toss the broccoli florets with sesame or avocado oil and a sprinkle of salt.
Place the salmon fillets skin-side down in the air fryer basket and arrange the broccoli florets around them (or cook in batches if needed).
Air fry at 400°F (200°C) for 8-10 minutes, until the salmon is cooked through and the broccoli is crisp-tender.
During the last 2 minutes of cooking, brush the salmon with the remaining teriyaki sauce to build a glossy, caramelized coating.
Remove from the air fryer and let the salmon rest for a few minutes to redistribute juices. Serve with broccoli, garnished with toasted sesame seeds and chopped green onions if desired.