Place fish in a single layer in a greased 12- x 8- x 2-inch baking dish. Sprinkle lemon juice and pepper over fish. Set aside.
Cook bacon until crisp; drain well on paper towels, and reserve drippings in skillet. Crumble bacon, and set aside. Sauté onion in bacon drippings over low heat until tender. Place sautéed onion on fish.
Combine reserved bacon, breadcrumbs, and parsley; sprinkle over fish. Bake, uncovered, at 350° for 25 minutes or until fish flakes easily when tested with a fork. Serve immediately.