Cut the courgettes in half lengthways, and then into 3 (about 6cm pieces). In a baking tray, toss with a glug of oil, garlic, sprigs of thyme, salt and pepper. Place skin side down, and roast for 30–40 minutes until golden and softened.
Transfer to board, and squeeze the garlic cloves out of their skins (discard the skins). Roughly chop everything till it looks like a chunky dip. Mix in the lemon juice, tahini, herbs and season to taste. Stir in a spoon of natural yoghurt and serve as a dip or delicious accompaniment to meat and fish.