Season monkfish chunks with salt. In a medium to large pot of water boil bay leaves, 1/2 stalk celery, and small onion for 5 minutes. Add monkfish and cook for an additional 10 minutes. Drain and place monkfish in large bowl; set aside. Discard celery, onion, and bay leaves.
In large frying pan, saute the celery pieces in vegetable oil until tender; add to fish. Saute red and green pepper pieces, add to fish. Saute the 3 sliced onions for about 5 minutes; add the tomato paste, alternating with the vinegar. Mix well; add sugar and olive pieces and cook for an additional 10 minutes, stirring frequently. Season with salt and pepper. Add vegetable mixture to monkfish and refrigerate. Best when served chilled.
Recipe courtesy The Taste of Gloucester: A Fisherman's Wife Cooks, Gloucester Cookbook Committee, 1976