Zest and juice half your lemon into a large bowl. Squeeze in the tahini. Pour in 2 tbsp cold water and 1 tbsp oil. Whisk with a pinch of salt till smooth and creamy. Spoon in half the pot of yogurt and swirl it through the tahini dressing.
Finely chop the mint leaves and fold those through the tahini yogurt. Taste and season. Add more lemon to taste.
Set a griddle or frying pan on a high heat. Cut the mini romaines in half, slicing through the root, to keep all the leaves together. Pull off any tatty outer leaves.
Rub 1 tsp oil onto the cut-side of each romaine and sprinkle with salt. Place cut side down into the hot griddle pan and cook for 5 mins till charred and softened.
Place the charred romaines onto a serving platter. Drizzle over the tahini yogurt. Scatter over the dill leaves.