Thinly slice the leek.
Heat the oil in a large saucepan and gently sauté the leeks for about 8 minutes.
Meanwhile chop the potatoes & carrots (no need to peel them, if organic) and shred one large cupful of spring greens.
Add the carrots and potatoes to the leeks, then cook for another 5 minutes (under cover).
Pour over the stock, bring to the boil, then simmer over low heat for 15 minutes until the vegetables are tender.
Add the spring greens and peas, bring to the boil again and simmer for five minutes.
Make the gremolata: mix the parsley, lemon zest and garlic in a small bowl.
Ladle the soup into 4 bowls, and add some gremolata and a squeeze of lemon juice to each.
Serve immediately.