In a small bowl, whisk the cornstarch and water together until completely smooth.
Add the orange juice, orange zest, soy sauce, brown sugar, ginger, garlic, sesame oil, and cornstarch mixture to a small saucepan.
Bring the sauce to a gentle simmer over medium-low heat. Cook for 3–5 minutes, stirring regularly, until it lightly thickens. Remove from the heat and allow it to cool slightly.
Preheat the oven to 400°F (200°C). Line a baking sheet with foil and lightly oil the surface.
Arrange the salmon fillets on the prepared baking sheet. Generously brush them with the orange teriyaki sauce, reserving approximately half of the sauce for finishing and serving.
Bake the Orange Teriyaki Salmon for about 12–14 minutes, or until the salmon is opaque and flakes easily with a fork. Cooking time may vary depending on the thickness of the fillets.
Brush the cooked salmon with more sauce. Place it under the broiler for about 1 minute, watching carefully, until the glaze becomes glossy and lightly caramelized.
Serve over steamed rice and garnish with sesame seeds, chopped green onions, and red pepper flakes, if desired.