Mix the soy sauce and sugar in a resealable plastic bag and add already portioned 6 oz. wild Alaska sablefish fillets. Seal the bag and turn it several times to evenly distribute the marinade; refrigerate for at least 4 hours (24 hours maximum).
Make braised onions
Meanwhile, make the braised red onions: Cook the bacon in a large saucepan until it renders and begins to crisp. Pour off half the fat. Add the red onions to the pan along with the wine, soy sauce, thyme, brown sugar and vinegar. Cook over medium heat, stirring occasionally, until all the liquid boils away and the onions are tender, about 15 minutes. The onions can be refrigerated until you are ready to bake the fish.
Prepare panko crust
Toss the panko or bread crumbs with the parsley, thyme and melted butter in a mixing bowl.
Assemble and serve
When ready to assemble, preheat the oven to 350ºF. Reheat the braised onions in a saucepan and spread them out in a large shallow baking dish. Lift the fish fillets from the marinade and arrange them on top of the onions, skinned side down. Top each fillet with an even coating of the crust mixture, gently patting it on with your fingertips. Bake for 25 to 30 minutes, or just until the fish flakes apart slightly when nudged with your finger and the interior is no longer translucent. Turn the broiler to high and broil until the crust is golden brown. Remove from heat and let stand 5 minutes. Serve with mashed or roasted winter squash, or braised winter kale.