Cut the avocados in half, remove the stone, and brush with olive oil all over. Season the flesh with salt and pepper, and put onto the grill. Don’t move the avocado halves as the flesh might stick, just leave it for 2-3 minutes until the avocado releases itself from the grill. Add the lemon halves to the grill to char. Put the avocados onto a platter, squeeze over the burnt lemon, spoon the harissa hummus into the middles, then drizzle over the tahini yogurt. Scatter with more coriander and a spoon of harissa if you like. Serve with flatbreads and any remaining hummus.