Heat a large skillet over medium-high heat and add 1 tablespoon of the EVOO, 1 turn of the pan, and 1 tablespoon of the butter. When the butter melts into the olive oil, add the cabbage and cook for 3 minutes to wilt it a bit. Season the cabbage with salt and pepper and add 1/2 cup of chicken broth. Reduce the heat to medium-low and cook for 10 minutes, stirring occasionally.
Score the skin of the fish and season with salt and pepper. Heat a medium nonstick skillet over medium-high heat and add 1 tablespoon of the EVOO, 1 turn of the pan. When the oil ripples, add the fish, skin side down, and cook for 4 minutes on each side. The skin will be crisp; the flesh will be opaque. Remove the fish to a platter and cover with foil to keep warm. Return the pan to the stove and add the remaining 1 tablespoon of EVOO, 1 turn of the pan, and the shallot. Cook for 2 minutes, then add the grapefruit and warm through. Add the wine and reduce for 1 minute, then add 2 tablespoons of the butter. Turn off the heat; shake the pan to combine.
Bring the remaining 1 cup of broth and 1 tablespoon of butter to a boil in a medium saucepan with a lid, then add the couscous, peas and chives. Turn off the heat, stir and cover with the lid. Let stand for 5 minutes, then uncover and fluff with a fork. Transfer to a serving dish.
Place the cabbage in another serving dish. Uncover the fish, top with the grapefruit sauce and serve.