We peel the potatoes, rinse and coarsely chop them. Put them in a pot, add the 5 cups of water, salt to taste and boil for about 20 minutes.
In the meantime we prepare the remaining vegetables: peel the onions, rinse and coarsely chop them.
To clean the zucchinis, we cut off their two ends and then scratch their surface with a knife, to remove the outer layer. Rinse, drain and cut each into 3-4 pieces.
Remove the stem and seeds of the peppers, rinse and coarsely chop them.
We add to the pot the zucchinis, peppers, Santorini tomatoes, onions, celery and continue boiling for an additional 10 minutes.
In the meantime, we put in a bowl the olive oil, lemon juice and mix to combine.
Then we add to the pot the fish fillets, pour over the “ladolemono” (oil/lemon mixture) and boil for about 10-15 more minutes, until both vegetables and fish are tender. We may add some more boiling water if necessary.
We remove the pot from the heat and serve the “psari vrasto me lahanika”. We may pour over some of the stock and add pepper to taste.