Preheat oven to 400 degrees F. Spray a 9x13- inch baking dish with nonstick cooking spray; set aside.
In a small saucepan over medium heat, whisk together soy sauce, brown sugar, apple cider vinegar, garlic, sesame oil, salt and pepper. In a small bowl, whisk together water and cornstarch then gradually whisk into saucepan.
Bring to a boil and let boil for 1-2 minutes or until mixture starts to thicken. Reserve 1⁄4 cup of sauce; set aside.
Place the salmon in prepared pan and pour sauce on top (still reserving 1/4 cup). Bake for 15 minutes, or until salmon is flaky and cooked through.
Remove from oven and top with reserved sauce. Garnish with green onion and sesame seeds.