Heat the olive oil in a large pot over medium-high heat. Add the lamb cubes and brown them on all sides for about 6 minutes. Remove the lamb and set it aside.
Add the onion to the same pot and cook for 4 minutes until softened. Stir in the garlic and cook for 1 minute more.
Return the lamb to the pot. Add the harissa paste, cumin, coriander, and cinnamon stick. Stir everything for 2 minutes to coat the meat.
Pour in the diced tomatoes and beef broth. Season with salt and black pepper. Bring the mixture to a boil, then lower the heat, cover, and simmer for 1 hour until the lamb is tender.
Add the okra pieces and cook uncovered for 15 minutes until the okra is tender but still holds its shape.
Remove the cinnamon stick. Sprinkle with chopped parsley and serve with lemon wedges on the side.