2) Add the onion to the pan, and cook, stirring until wilted, about 3 minutes. Stir in the cabbage and cook until wilted, about 2 minutes.
3) Add the water, mustard, vermouth, thyme and allspice, and season with 0.5 tsp salt and pepper, to taste. Cover and cook until soft and fragrant, about 8 minutes more. (This can be done up to 1 hour ahead and then reheated, covered, to serve.)
4) Pat the fish dry and season with the remaining 0.5 tsp salt and pepper, to taste.
5) Heat a large nonstick skillet over a high heat and add the reserved bacon fat to the pan. Lay the fish, skin-side up, in the pan and cook until golden brown, about 6 minutes. Turn the fish over and continue to cook over a medium to medium-high heat until the fish is opaque but not flaking, about 4 minutes more.
6) Divide the cabbage among 4 plates, place the fish browned side up on top and drizzle any juices over the fish. Serve.