Prep the pork: Pat the pork tenderloin dry with paper towels. Trim any visible silver skin so the meat stays tender and cooks evenly.
Make the marinade: In a bowl, whisk soy sauce, honey, brown sugar (if using), garlic, vinegar, oil, Dijon, smoked paprika, pepper, salt, and red pepper flakes. Taste and adjust sweetness or salt as needed.
Marinate briefly: Place the pork in a zip-top bag or shallow dish.
Pour in half the marinade and coat well. Reserve the other half for glazing. Marinate for 15–30 minutes at room temp, or up to 4 hours in the fridge.
If chilled, let it sit out 15 minutes before cooking.
Preheat the air fryer: Set to 380°F (193°C) for 5 minutes. Lightly oil the basket to prevent sticking.
Air fry, round one: Place the pork in the basket. Air fry at 380°F for 10 minutes.
Glaze and flip: Brush with some of the reserved marinade, flip, and brush the other side.
Air fry another 6–10 minutes, glazing once more halfway through. Target internal temp: 140–145°F (60–63°C) at the thickest point.
Rest the meat: Transfer to a cutting board, tent loosely with foil, and rest 5–8 minutes. This keeps it juicy and lets it finish cooking gently.
Thicken the glaze (optional): Pour the remaining marinade into a small pan. Bring to a simmer.
Stir in cornstarch slurry and cook 30–60 seconds until glossy. Never use raw marinade without boiling it first.
Slice and serve: Slice the pork into 1/2-inch medallions. Spoon the thickened glaze over the top. Garnish with sesame seeds and green onions if you like.