Prep work: Preheat the oven to 400°F. Line a 9x13-inch pan with parchment paper. Alternatively, you can coat it with non-stick spray. Arrange the salmon fillets in the pan so that they are close but not touching, skin side down.
Make cornstarch slurry: In a small bowl, whisk together the water and cornstarch.
Combine sauce ingredients: In a small saucepan, whisk together the brown sugar, soy sauce, lemon juice, garlic, ginger, and sesame oil. Slowly whisk in cornstarch slurry into the mixture.
Cook the sauce: Heat the teriyaki sauce over medium-high heat until it comes to a boil. Reduce heat until it can maintain a gentle boil and allow to cook for about 2 minutes until the mixture just starts to thicken. Remove from heat.
Bake salmon: Remove about 3 tablespoons of the sauce and reserve for later. Pour or brush the remaining sauce over the salmon fillets. Bake in preheated oven for 12-16 minutes or until salmon is flaky and cooked through. Bake times may vary by the thickness and initial temperature of salmon. salmon is considered cooked when the thickest part reaches 145°F when checked with an instant-read thermometer.
To serve: Brush the top of the salmon with the reserved sauce. Garnish with green onion and sesame seeds. Serve with rice and a steamed vegetable.