Mix the oil, vinegar, mint and seasoning. Brush the dressing over the lettuce heads.
Heat a griddle pan to smoking point, then place the lettuce, cut-side down, on the pan. Grill for 1–2 minutes until lightly charred.
To make the yoghurt, mix all the ingredients, adding a dash of hot water if it’s too thick.
Pipe or dollop the sumac-tahini yoghurt over the grilled lettuce, then sprinkle with the pomegranate rubies and garnish with mint leaves.