For the lamb shoulder and chickpeas: Heat the oven to 325 degrees F. Place the lamb shoulder in a Dutch oven and season all over with salt and pepper. Halve the lemon, then coarsely chop half and cut the other half into wedges for serving.
In a food processor, blend the chopped lemon, jalapeño, garlic, fennel seeds, and 1 tablespoon salt until combined. Add three-quarters of the dill, parsley, and scallions, and blend until a coarse, wet paste forms. (Put the remaining herbs in the fridge until serving.)
Smear the herb paste all over the lamb shoulder, turning it in the Dutch oven if necessary. Pour 1 cup of water into the Dutch oven, cover, and bake until the shoulder falls apart easily when prodded with a fork, about 3 hours.
Then, increase the oven heat to 400 degrees F. Uncover the pot and add the chickpeas to the braising liquid around the lamb. Roast until the lamb is golden brown, about 25 minutes.
While the lamb is browning, prepare the dates: Blend the toasted fennel seeds in a spice or coffee grinder or food processor until coarsely ground. Mix with the flaky salt and transfer to a small serving plate. In a small cast iron skillet over high heat, char the dates until black in spots, about 3 minutes. Toss the dates in the fennel salt.
To serve the lamb and chickpeas, remove the kitchen twine, if using, then slice the lamb shoulder. Skim off any fat from the braising liquid in the pot. Serve the lamb over the chickpeas and braising liquid. Garnish with remaining fresh herbs and lemon wedges, for squeezing over. Season to taste with salt and pepper and serve with charred dates.