Preheat oven to 150C. Place a rack in a large roasting tray. Use a small, sharp knife to make shallow cuts on the surface of lamb. Season. Heat 2 teaspoons oil in a large frying pan over high heat. Add the lamb and cook, turning, for 5 mins or until browned all over. Remove from heat.

Combine Cajun seasoning, lemon zest, 1 garlic clove, salt and 2 tablespoons oil in a medium bowl. Add the lamb and turn to coat. Place lamb on rack in the roasting tray. Pour stock into the tray. Cover with foil and roast for 3-3 1/2 hours or until the lamb is browned and very tender. Remove the foil and shred meat with a fork.

Meanwhile, heat rice following packet directions. Heat remaining oil in a medium saucepan over medium heat. Add the celery and cook, stirring, for 5 mins. Add remaining garlic, spring onion and extra Cajun seasoning and cook, stirring, for 2 mins or until fragrant. Add rice, chopped coriander and lemon juice and stir to combine. Season.

Divide rice mixture among tortillas. Top with lamb, capsicum, coriander leaves and a dollop of yoghurt. Roll to enclose filling.