Heat a large skillet over medium-high heat with 1 tablespoon extra-virgin olive oil, 1 turn of the pan and 1 tablespoon butter. When butter melts into oil, add the cabbage and cook 2 to 3 minutes to wilt it down a bit. Season with salt and pepper and add 1/2 cup chicken stock to the skillet. Reduce heat to medium low and cook 10 minutes, stirring occasionally.
Cut ends off citrus, either grapefruit or oranges. Stand the citrus upright and trim away peel in strips with a small sharp knife cutting from top to bottom, spinning the citrus around as you work. Once cleaned of skins, cut the sections of the fruit away from the membranes.
Season the fish with salt and pepper and grapefruit or orange zest. Heat a nonstick skillet over medium-high heat with 1 tablespoon extra-virgin olive oil, 1 turn of the pan. When oil ripples, add fish. Cook fish 3 to 4 minutes on each side, skin side down first. Skin should be crisp and flesh should be opaque. Remove fish to a platter and cover with foil to keep warm. Return pan to stove top and add another tablespoon extra-virgin olive oil, 1 turn of the pan, and the shallots. Cook shallots 2 minutes then add the citrus to the pan and warm through a minute. Add white wine and reduce 1 minute then add a tablespoon of butter. Turn off heat. Shake pan to combine butter with citrus.
While the sauce is working, bring 1 1/2 cups chicken stock, 1 tablespoon butter and a drizzle of olive oil to a boil in a medium pot with a tight fitting lid. When stock boils, add couscous, peas and chives to pot. Turn off heat, stir and set lid in place. Let stand 5 minutes then uncover and fluff with a fork. Transfer to a serving dish.
Place cabbage in a serving dish. Uncover fish. Pour citrus and sauce over fish and serve.