2 tablespoons low-sodium soy sauce
1 tablespoon olive oil
1 large red onion, cut into 1/4-inch thick wedges
1 pinch kosher salt and ground black pepper to taste
4 (5 ounce) skinless salmon fillets
Set an oven rack about 6 inches from the heat source and preheat the oven's broiler. Combine brown sugar and soy sauce in a small bowl. Heat oil in a pan over medium-high heat. Saute onion, salt, and pepper in the hot oil until soft, 5 to 7 minutes. Transfer to sugar mixture and mix together. Place salmon fillets on a rimmed baking sheet. Cook salmon in the preheated oven for 10 minutes. Turn over and drizzle with 1/2 of the sugar mixture. Continue to broil until salmon is opaque throughout and easily flaked with a fork, 5 to 10 minutes more. Serve with remaining sugar mixture.