Heat your oven to 220°C fan/240°C/gas mark 9.
Brush a baking sheet with olive oil. Cut the aubergines in thick slices (about 2cm), place on the baking sheet, then brush the cut surfaces with a bit more oil. Season with salt and pepper and roast for 25–30 minutes until golden and really soft when pressed.
Blitz the preserved lemon skin with the basil, parsley, marjoram and garlic until it forms a paste (you can use a blender or a meat grinder). Tip the paste into a bowl, then use a spoon to stir in the oil, vinegar, salt and pepper to make a salsa.
Sprinkle the pitta breads with a little water and pop them in the oven to warm for 40–50 seconds. Remove and slit each one to open into a pocket.
Put a generous tablespoon of tahini and 4 slices of tomato in each pitta. Pour the salsa over the warm aubergines. Divide them between the pitta pockets and serve warm.