From the cookbook Mediterranean Food of the Sun. Their introduction reads "This is a traditional Greek preparation for fish, using onion, tomatoes, parsley and olive oil. Although cod is an Atlantic fish it works very well with this fish."
Heat the oil in a large saute pan. Add the onions and cook until pale golden.
Add the tomatoes, garlic, sugar, dill, mint, celery leaves and parsley with 1 1/4 cups of water. Season with salt and pepper, then simmer,uncovered, for 25 minutes, until the liquid had reduced by one-third.
Add the fish steaks and cook gently for 10-12 minutes, until the fish is just cooked.
Remove from the heat and add the lemon juice.
Cover and let stand for about 20 minutes before serving.
Arrange the cod on a serving dish and spoon the sauce over. Garnish with the herbs.