Pre-heat a char-grill on high heat. Cut eggplant in half lengthways. Prick skin all over with a fork. Drizzle with 2 tbsp olive oil. Char-grill eggplant, turning occasionally, for 15-20 minutes until skin has blackened and flesh is soft. Transfer to a heatproof bowl. Cover with plastic wrap and stand for 10 minutes, until cool enough to handle. Peel and discard skin.
Place eggplant flesh in the jug of a blender. Add lemon juice, garlic, tahini and Fountain Barbeque Sauce, blend until almost smooth.
Meanwhile, combine cumin, coriander, sumac and remaining oil on a large flat plate. Roll lamb in the spice mix to lightly coat. Char-grill lamb for 3 minutes each side for medium, or until cooked to your liking. Transfer to a plate. Cover with foil and rest for 5 minutes. Slice.
Arrange lamb on a serving plate. Serve with eggplant puree and salad.