Start by trimming the dark green tops and root ends of the leeks. Carefully slice them lengthwise and rinse thoroughly to remove any dirt trapped between layers. Then, boil them briefly until they soften and become pliable for stuffing.
Once softened, gently peel apart the leek layers without tearing them. These layers will act as natural wrappers for your filling. Keep them aside on a clean surface, ready to be filled.
In a bowl, combine ground beef, uncooked rice, chopped onion, olive oil, tomato paste, and spices. Mix everything well until evenly combined. The mixture should feel moist but not overly wet.
Take a leek layer and place a small amount of filling inside. Roll it up tightly, similar to a stuffed roll. Repeat the process with all layers until the filling is used up.
Place the stuffed leeks neatly in a pot. Pour water or broth over them and drizzle lemon juice on top. Cover and let them simmer on low heat until the rice is fully cooked and the flavors meld together.