Heat the oven to 220˚C (425˚F).
Lay the leeks in a 20cm x 30cm ovenproof dish, pour two tablespoons of oil over the leeks and season with one teaspoon of salt, and a sprinkling of pepper.
Roast for 25 minutes, until the leeks are soft and starting to caramelize.
Meanwhile, bring a small saucepan of water to a boil, blanch the edamame beans for three minutes, then drain.
Add the edamame to the cooked leeks, then add the basil, mint, lemon zest and Parmesan, and toss gently.
Add pieces of Mozzarella, and serve straight from the roasting dish or transfer to individual plates.
Just before serving, drizzle with olive oil, lemon juice and a sprinkle of fleur de sel.