Preheat oven to 350 degrees F. Place fish fillets in large glass or ceramic ovenproof baking dish.
Lightly spray a nonstick skillet with cooking spray and heat over medium-high heat.
Sauté the onion until golden brown; then add the peaches, orange juice, allspice, and low-sodium soy sauce. Bring to a boil and cook briefly, about 2 minutes.
Pour the sauce over the fish and place in the oven.
Bake the fish until done and fork-tender, about 10 minutes.
Serve immediately with the sauce spooned over the top of each fillet.