Salt the swordfish well and set aside at room temperature.
Cut the onion in half and grate it through a rough grater. Chop the celery stalk very finely – or run it through the grater.
In a large frying pan or wide, shallow pot, heat the olive oil and sauté the onions and celery gently for 3-4 minutes over medium heat.
Add the tomatoes, white wine, capers, bay leaf and olives. Mix well and bring to a simmer. Simmer uncovered until it gets thicker, about 10 minutes. Taste for salt and add some if needed.
Dust the swordfish in the semolina or regular flour. Semolina is a traditional Southern Italian flour used to make pasta - can be found in large supermarkets or specialty groceries stores.
Lay the swordfish on the sauce and spoon a little over the fish. Sprinkle the vinegar over it all and cover. Let this cook over medium heat for 6-8 minutes, then uncover and cook for another 3-4 minutes.
To serve, gently lift the swordfish out and set aside. Spoon some sauce on a plate and place pieces of the fish on top. Garnish with chives or celery leaves.