Heat oil in a pan and cook onion and garlic over medium heat until softened (3-4 minutes). Add orange juice and saffron and bring to the boil. Add carrot and turnip, reduce heat to low and simmer until juice reduces slightly and vegetables are tender (10-15 minutes).
Place mullet skin-side up in a lightly oiled deep-sided tray. Pour over orange juice mixture, season to taste, cool, then cover with plastic wrap and refrigerate until well chilled (2½-3 hours). Serve mullet and vegetables drizzled with marinade and scattered with shiso cress.
Note Red mullet is often sold as a whole fish. Ask your
fishmonger to clean and fillet it for you. You may need to order it