Heat the olive oil in a large Dutch oven over medium-high heat. Add the lamb cubes and brown them on all sides, about 6 to 8 minutes total. Remove the lamb to a plate and set aside.
Add the chopped onions to the same pot and cook until softened, about 5 minutes. Stir in the minced garlic, turmeric, and cinnamon and cook for 1 minute until fragrant.
Return the browned lamb to the pot. Pour in the beef broth and pomegranate molasses. Add the salt and black pepper. Bring the mixture to a boil, then reduce the heat to low, cover, and simmer for 1 hour and 15 minutes.
Stir in the chopped walnuts and continue simmering uncovered for 15 more minutes until the sauce thickens slightly and the lamb is fork-tender.
Ladle the stew into bowls and sprinkle with the chopped parsley before serving.