Preheat the oven to 180C / 170C fan / gas 4
Cut the neck fillets into equal sized pieces and thread onto a skewer lengthwise through the middle of each piece. With a sharp knife, make 1 inch slashes down the length of each skewered piece.
For the marinade, combine the garlic, cumin, coriander, chilli flakes, lemon juice and il in a small bowl. mIx to combine and rub over the skewered lamb fillets. Cover and refrigerate for an hour.
For the sauce, slice off the top of the garlic head. Place cut side up on a oven tray, drizzle with olive oil and sprinkle with salt and pepper. Roast int he preheated oven until very soft, approx 15/20 minutes.
Leave until cool enough to handle and then squeeze out the loves into a food processor or blender. Add the mustard, vinegar, cream, parsley and yoghurt and pulse until smooth. Season to taste.
To grill the lamb preheat the grill or a grill pan. Grill, turning every 2 minutes around 8 minutes for medium rate and 12 minutes for well done.
Sprinkle the lamb with salt and pepper, serve hot with the garlic yoghurt sauce on the side and a big salad.