Heat half the olive oil in a large skillet or frying pan over medium-high heat. Season the lamb with salt and pepper and, in batches if needed, cook until browned. Remove from the pan and set aside.
In the same pan, add the remaining oil. Sauté chopped onion and garlic for 3-4 minutes until softened.
Transfer the browned lamb back to the pan. Add tomato paste, ground cumin, sweet paprika, ground cloves, bay leaf, beef broth, diced tomatoes, and cilantro. Stir well and transfer the mixture to a large slow cooker. Stir in chickpeas and lentils.
Cover the slow cooker and cook on low for approximately 6 hours or until the lamb is tender, and the stew has thickened.
In a pitcher, combine water and cucumber slices. Let it infuse in the refrigerator for at least 10 minutes before serving. Serve over ice if desired.
Serve: Garnish the lamb stew with cilantro and Greek yogurt, and serve with toasted pita bread. Enjoy with cucumber water.