For the spice mixture
Whisk the olive oil, lemon juice, cumin, sumac and oregano together. Season well.
Slice the aubergines into 1cm slices and grill on a smoking-hot griddle pan until charred and soft. Brush with the spice mixture as soon as they come off the pan.
Heat a large saucepan and add the remaining spice mixture. Sauté the garlic and the rest of the spices for 1 minute over a low heat then add the dates, pomegranate molasses and tomatoes. Fill the tomato tin with the water, swirl around and add it to the saucepan. Simmer for 30 minutes. Add half the walnuts, parsley and season well.
Preheat the oven to 180°C, gas mark 4. In a 20cm x 30cm large ovenproof dish, layer the aubergines and tomato sauce alternatively, stopping halfway to crumble in ²∕3 of the feta.
Finish with a layer of sauce and feta and the rest of the walnuts. Bake for 30 minutes until golden.