Heat the oven to 425 degrees F. Scrub the sweet potatoes and halve them lengthwise.

Rub the cut faces with 1 tablespoon of the olive oil and a pinch of salt and lay them cut side DOWN on one half of a sheet pan.

Drain and rinse the chickpeas and roll them dry in a clean towel until they squeak. Wet chickpeas steam instead of crisping.

Toss the dry chickpeas with the remaining 2 tablespoons olive oil, the cumin, coriander, smoked paprika, salt and pepper. Spread them in a single layer on the other half of the pan.

Roast 25 to 30 minutes, until a skewer slides easily into the thickest part of the potatoes and the chickpeas rattle when you shake the pan.

Whisk the tahini, 3 tablespoons lemon juice, grated garlic, dried dill and salt together in a small bowl. The mixture will seize into a thick pale paste. This is normal.

Add cold water 1 tablespoon at a time, whisking hard after each addition. Around 4 tablespoons it loosens and turns smooth and glossy.

Keep going up to about 6 tablespoons total, until the sauce pours off the whisk in a ribbon. Taste and add salt and lemon, it should taste too lemony on its own.

Put the chopped red onion in a bowl with 1 tablespoon lemon juice and a pinch of salt and leave 5 minutes. Add the parsley, cherry tomatoes and cucumber and toss.

Set two roasted potato halves on each plate cut side up. Fluff the flesh with a fork, press a shallow trough down the middle and season the exposed flesh with salt.

Spoon the roasted chickpeas into the trough, pour the lemon tahini sauce over so it runs down into the flesh, and add the raw parsley topping last.

Finish with a squeeze of lemon from a wedge and serve immediately while the potato is still hot.