Prepare all of your ingredients by dicing the onion, carrots, celery, and zucchini into 1-2cm cubes. Cut the potatoes into quarters, rinse the dried brown lentils, chop the rosemary finely, and chop the kale.
Heat a large pan (or a searing friendly instant pot/slow cooker) over medium-high heat and add a splash of olive oil. Season the lamb well all over with salt and pepper, then brown it on all sides until a golden crust forms, about 5 minutes. If you are using a slow cooker - transfer the lamb into it, or if you are searing in a slow/pressure cooker, simply it put aside.
In the same pan, add the diced onion, carrots, celery, and minced garlic. Sauté for about 5 minutes, until they begin to soften and the onion becomes translucent.
Then add the sumac, smoked paprika, cumin, allspice, and cinnamon to the pan/pot. Stir well to coat the vegetables with the spices and cook for another minute or so until fragrant.
Pour in the red wine to deglaze and let it simmer for 2-3 minutes so it will reduce slightly.
If using a slow cooker, transfer the sautéed vegetables and wine mixture to the slow cooker with the lamb. Then add everything else - the diced zucchini, cherry tomatoes, potatoes, kale/spinach, lentils, and dates. Pour in the beef bone broth and stir well to combine.
Cover the slow cooker and cook on low for 8 hours, or until the lamb is tender and falling apart and the vegetables are cooked through.
Taste and adjust seasoning with additional salt and pepper if needed. Serve the braised lamb shoulder casserole hot, with crusty bread for dipping.