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.