Heat the oil in a pan and gently fry the onion and garlic for 2-3 minutes.
Add the leeks and potatoes and continue cooking for a further 3-4 minutes.
Pour in the stock and bring to a simmer. Simmer for around eight minutes, or until the potatoes are still firm but nearly cooked through.
Add the lemon zest, cherry tomatoes and chunks of fish and cook for 3-4 minutes, or until the fish and potatoes are cooked through.
Stir in the chopped parsley and serve.
