For the marinade, clean the chilli peppers, cut lengthwise, remove seeds, wash and cut into fine rings. Wash the thyme and remove the leaves. Mix the chilli rings, thyme, zatar, olive oil and 1-2 teaspoons of salt.
Preheat oven (electric cooker: 220 °C/circulating air: 200 °C/gas: see manufacturer). Line two baking trays with baking paper. For the vegetables, drain the chickpeas and place them on a baking tray. Wash sweet potatoes, cut lengthwise into coarse slices. Clean and wash the aubergines and cut them in half lengthwise. Put them with sweet potatoes on a second baking tray. Sprinkle the marinade on the chickpeas, eggplants and sweet potatoes. Bake together in a hot oven for about 30 minutes. After about 15 minutes, change the baking trays.
Take the chickpeas out of the oven and turn on the grill. Bake aubergines and sweet potatoes on the middle shelf for another 8 minutes. Serve grilled vegetables with chickpeas and cress dip.