Prepare the Teriyaki Sauce: In a small saucepan, combine the soy sauce, fresh orange juice, water, honey, minced garlic, ginger, and chili flakes.

Thicken the Sauce: In a small bowl, mix the gluten-free flour with 1 tablespoon of water to make a slurry. Slowly add the slurry to the simmering sauce, whisking continuously until the sauce thickens slightly, about 2-3 minutes. Remove from heat and stir in the lemon juice.

Marinate the Salmon: Place the salmon fillets in a shallow dish and pour half of the cooled teriyaki sauce over the fillets. Let them marinate for at least 15 minutes, or up to 30 minutes, in the refrigerator.

Preheat the Oven: While the salmon is marinating, preheat your oven to 400°F (200°C).

Bake the Salmon: Remove the salmon from the marinade and place the fillets on the prepared baking sheet. Discard the used marinade. Place in the preheated oven and cook for 12 to 15 minutes, or until the salmon easily separates when tested with a fork.

Glaze and Garnish: During the last 5 minutes of baking, brush the remaining teriyaki sauce over the salmon fillets. Once done, remove the salmon from the oven and sprinkle with sliced green onions and sesame seeds.

Serve: Serve the baked teriyaki salmon hot, garnished with additional green onions and sesame seeds if desired. Serve alongside fluffy rice and lightly sautéed vegetables for a well-rounded dish.