HEAT OVEN to 400F/204C. Line a baking sheet, large enough to fit the trout, with parchment or disposable foil, sprayed with cooking oil (for easy clean up).
MAKE SAUCE/GLAZE: Whisk together all ingredients in a small glass measuring cup or bowl. If you want a slightly thicker glaze, whisk in the cornstarch and microwave sauce for 45-60 seconds. I do this. If you prefer a thin glaze, don't use the cornstarch.
PREPARE TROUT FILLETS: Generously sprinkle trout with salt and pepper. Sprinkle chopped green onions over fish. Drizzle on enough glaze to cover the fish, about half the sauce/glaze, reserving the rest for serving. Place fish, skin side down, on pan.
ROAST/BAKE TROUT: for 8-11 minutes depending on the thickness of the fish.
Remove from oven to a large flat dish and cut into portions. If you want to remove skin, slip a spatula between the bottom of the flesh and skin, then lift trout off. Drizzle on the remaining sauce and sprinkle parsley, green onions or other fresh herbs on maple balsamic trout if desired.