Preheat the oven to 450 degrees .
In a shallow bowl, season the flour with salt and pepper. Dredge the fish in the seasoned flour and shake off any excess.
In a 9-by-13-inch baking dish, toss the escarole, onion, sliced garlic and nutmeg; season.
In a small bowl, whisk the wine, stock and EVOO; pour half the wine mixture over the escarole. Arrange the fish on top of the greens.
For the gremolata, on a cutting board, finely chop the herbs with the lemon zest and chopped garlic. Sprinkle the fish with the gremolata, top with pats of butter, then pour the remaining wine mixture over the fish. Bake until the fish is opaque and cooked through, about 20 minutes.
Serve the fish in shallow bowls or deep plates on top of the greens. Garnish with the lemon wedges.