Heat oven to 220C.
Cut off and discard the top quarter of each garlic bulb to expose the cloves, then put the bulbs cut side up in the centre of a 25cm square of tin foil. Drizzle over two tablespoons of oil, sprinkle over a pinch of salt and a grind of pepper, then wrap the foil around the heads. Put the foil parcels on an oven tray and bake for 40 minutes, until the garlic is soft and caramelised, then remove and leave to cool.
While the garlic is cooking, put a griddle pan on a high heat and ventilate the kitchen. Once it’s very hot, grill the spring onions for eight to 10 minutes, turning them regularly, until blackened all over. Transfer to a board to cool slightly, then chop into roughly 3cm-long pieces and put in a large bowl.
Bring a medium saucepan of well salted water to a boil. Add the potatoes, cook for 10 minutes until tender, then drain.
Heat three tablespoons of oil in a large frying pan on a high flame, then fry the potatoes with half a teaspoon of salt and plenty of pepper for about 10 minutes, stirring every once in a while, until golden-brown and crisp. Tip the potatoes and their oil into the spring onion bowl, then add the peas, preserved lemon, mint and zest.
Squeeze the garlic out of its skins, add to the bowl with any of the oil, toss to combine and serve warm.