Prep the oven and pan: Heat your oven to 400°F (200°C).
Pat the salmon dry with paper towels and season lightly with salt and black pepper. Set aside.
Make the glaze: In a small bowl, whisk together orange juice, orange zest, honey, soy sauce, garlic, ginger, red pepper flakes, vinegar, and cornstarch until smooth. The cornstarch keeps the sauce glossy and thick.
Sear the salmon: Heat a large oven-safe skillet over medium-high heat.
Add oil. Place salmon in the pan, presentation side down (the side that was skinless or the prettier top). Sear for 2–3 minutes until golden.
Flip and add sauce: Turn the salmon gently.
Pour the glaze around the fish, not directly on top yet. Let it bubble for 30–60 seconds to start thickening.
Finish in the oven: Transfer the skillet to the oven. Bake 6–8 minutes, depending on thickness, until the salmon flakes easily and the glaze is sticky and shiny.
Spoon sauce over the top during the last minute for extra gloss.
Check doneness: If you use a thermometer, pull the salmon at 125–130°F for medium, or up to 135°F for a bit more done. It will rise a couple of degrees as it rests.
Garnish and serve: Spoon more glaze over each fillet. Top with sliced green onions and sesame seeds.
Add orange slices on the side if you like. Serve with rice, quinoa, or a simple green salad.