To make the dressing, whisk the tahini, garlic, honey, cumin, lemon zest and juice and a good pinch of salt in a small mixing bowl. Slowly whisk in three tablespoons of warm water until the dressing is of pouring consistency. If not, add another spoonful of water. Check the seasoning and set aside.
Cut each cabbage lengthways into 4 wedges leaving the base intact so that the pieces hold together. Rub the cabbage wedges with olive oil and season with salt.
Heat a grill pan over a high heat. When hot add the cabbage wedges and sear for 4-5 minutes on each cut side, then carefully turn onto the curved side and cook until soft and charred but still retaining a little crunch.
Arrange the cabbage on a serving dish. Drizzle with dressing and scatter with mint, chillies and nigella seeds. Pour any remaining dressing into a small bowl and serve with the cabbage.
