Place 4 wooden skewers in a tray of water to soak.
Place the lamb and spices (if using) into a big bowl, pick in the thyme leaves and finely grate in the lemon zest, then scrunch and mix together well.
Divide the mixture into 4 equal pieces. With damp hands, shape the meat around and along each skewer, pressing little indents into the meat as you go, for a nice texture.
Grill the kebabs on a barbecue for 8 to 10 minutes, or until golden and cooked through, then push to the cool side and warm your tortillas next to them for 30 seconds (you can cook everything on a griddle pan or under the grill, if you prefer).
Transfer the tortillas to plates and top each with a little lettuce. Drizzle with olive oil and a squeeze of lemon juice, if you like.
Slip the meat off the skewers and break it up, add a dollop of yoghurt and drizzle over any resting juices. Finely chop and sprinkle with chilli (deseed if you like) for an extra kick, then tuck in. Delicious!