In a mixing bowl whisk together the maple syrup, soy sauce, and minced garlic until combined.
Place the salmon fillets in a baking dish and pour the maple-soy mixture evenly over them.
Cover and refrigerate the salmon for 30 minutes, turning the fillets once halfway through to marinate evenly.
About 10 minutes before the marinade is finished, preheat the oven to 400°F (200°C). Lightly spray or grease a 13x9-inch baking dish.
Transfer the marinated salmon to the prepared baking dish, reserving the marinade; bake in the preheated oven until the salmon is cooked through, about 15 minutes.
While the salmon bakes, pour the reserved marinade into a small saucepan and bring to a boil over medium-high heat, stirring frequently.
Once boiling, reduce the heat slightly and simmer, stirring frequently, until the marinade is reduced to about 1/4 cup and slightly thickened (a few minutes).
Serve the baked salmon warm with about 1 tablespoon of the reduced maple-soy glaze drizzled over each fillet and sprinkle with freshly ground black pepper and chopped green onions if desired.