For tahini sauce:
Place the ground beef, onion, garlic, bread crumbs, egg, cilantro, basil, lemon zest, walnuts, cinnamon, cardamom, turmeric, salt and pepper in a large bowl. Mix everything together using your hand, until well mixed.
Shape the meat mixture into small meatballs.
Heat 3-4 tablespoons oil in a large non-stick frying pan over medium-high heat. Brown the meatballs on all sides (Do not crowd the pan by stacking the meatballs. Cook in a single layer. Do not over-cook). Add more oil if needed.
Preheat oven to 350 degrees F. Line a large baking dish with parchment paper. Place the meatballs on a baking dish and bake for about 12 minutes, or until cooked through.
Meanwhile make the sauce by mixing the tahini and lemon juice, and then adding enough water to make a thin sauce (I added about 2/3 cup water) . Salt it to taste.
Pour the tahini sauce over the meatballs and garnish with cilantro and walnuts.