Put the burghul in a saucepan and pour over the hot stock. Cover and leave to stand for 15 minutes.
Meanwhile, soak eight bamboo skewers in cold water to prevent them from burning under the grill.
Remove the lid from the pan and cook the burghul over a low heat for 4–5 minutes, stirring frequently, until the excess liquid has evaporated, but the mixture is still moist. Tip onto a tray, spread out and leave to cool.
Tip the cooled burghul into a bowl. Add the lamb, onion, pine nuts, coriander and dry spices and season to taste with salt and pepper. Thoroughly mix together with your hands. If you prefer a smoother-textured kibbeh, transfer the mixture to a food processor and blend for a few seconds. (You may need to do this in batches.)
Preheat the grill to medium. Divide the lamb mixture into 16 pieces and shape into oval-shaped balls (kibbeh). Thread the kibbeh onto the soaked wooden skewers, putting two on each skewer. Arrange, side by side, on a foil-lined grill tray and grill for 4–5 minutes on each side until well browned and cooked through. Remove and wrap loosely in the foil to keep warm.
Put the pita bread on the grill tray and grill for about 30 seconds on each side to warm them; don't let them brown or cook for any longer, or they will be too brittle to split open. Run a knife down one long edge of each pita and gently open out to make a pocket.
Half-fill the pita bread pockets with the shredded lettuce, carrot, cucumber and radishes. Slide the kibbeh off the skewers and divide among the pita pockets. Add more salad to taste. Drizzle each one with a spoonful of tzatziki and serve immediately.