Dry the shanks with a paper towel (dry meat browns, wet meat steams); place on a large, rimmed baking sheet; season shanks on all sides generously with salt and pepper.
Mix the rest of the rub ingredients together in a small bowl, massage into lamb. Cover and let stand at room temperature for 1 hour or, preferably, chill overnight then bring to room temperature.
Preheat oven to 350 F.
In a large Dutch oven, heat oil, over medium-high heat, until shimmering. Cooking in batches, add the shanks and sear on all sides, until golden brown, about 10 minutes. Transfer the shanks to a plate.
Add the garlic, cut side down, and cook, undisturbed, 2-3 minutes, until golden brown. Add the figs, 1/2 cup of grapes and shallots and cook, until the shallots begin to brown, about 4-8 minutes. Add Manischewitz wine, chicken stock, vinegar and whole spices (if using), scraping any browned bits off bottom of pan. Stir in the whole spices then arrange lamb shanks back into pot.
Cover, with a lid or aluminum foil, transfer shanks to oven and braise, turning them halfway through cooking, until meltingly tender, about 2½ - 3 hours (exact time will vary depending on shank). Add remaining 1/2 cup of grapes for the last 20 minutes of cooking time.
Carefully remove lamb shanks with tongs and transfer to a plate. Strain braising liquid and transfer figs, grapes, and shallots to a plate. Pour braising liquid back into the pot, with the garlic (optional: squeeze some of the garlic from the skin) and simmer, until braising liquid is thick enough to coat a spoon, about 30-40 minutes. Season to taste with salt and pepper (optional to discard the whole spices).
To make the couscous, heat olive oil in pan over medium-high heat until shimmering. Add couscous and cook, stirring often, until lightly browned, about 2-3 minutes. Add salt, chicken stock or water, and bring to a boil. Reduce heat to medium low, cover and simmer until couscous is al dente (slightly chewy and tender), and the liquid is absorbed; about 5-7 minutes (check your package directions for exact timing). If there’s any excess liquid, simply it drain it off. Fluff with a fork and let cool.
Toss couscous with 3/4 cup of fresh herbs, scallions, chilies (if using), lemon juice, salt and pepper.
To serve, spread couscous out on a serving platter. Arrange the lamb shanks, figs, grapes shallots and garlic on top. Spoon a generous amount of the braising liquid over shanks, top with remaining fresh herbs, freshly cracked pepper and flaky sea salt. Serve with additional braising liquid alongside for more drizzling. (Note: dish can also be served in individual serving bowls).