Preheat oven to 350°F.In a heavy Dutch oven or roasting pan with a tight-fitting lid, heat grape seed oil on medium-high. (NOTE: Use a Dutch oven that’s just large enough to hold the lamb pieces in a single layer.) On a wide plate, spread flour. Season lamb with salt and 1/4 tsp pepper, then dredge each piece in flour, shaking off any excess. Add lamb to Dutch oven and brown on all sides for 8 to 10 minutes; transfer lamb to a clean plate, uncovered.Reduce heat to medium and add onion, carrots and celery. Cook for 6 minutes, stirring frequently, until vegetables brown and soften slightly. Add garlic when vegetables are nearly softened. Add wine and bring to a boil; boil briskly for about 3 minutes, using a wooden spoon to scrape up any browned bits from bottom of Dutch oven. Add stock and return to a boil. Add tomatoes and their juices, thyme, basil, bay leaves, parsley and remaining 1/4 tsp pepper. Simmer for 1 minute on medium; remove from heat.Skim any fat from top of vegetable-wine mixture. Place pieces of lamb side by side in Dutch oven among vegetables and liquid. (NOTE: The liquid should come up to the top of the pieces but shouldn’t cover lamb. If necessary, add a bit of additional stock or water.) Place Dutch oven on medium heat and bring to a simmer. Cover pot tightly and transfer to middle rack in oven. Cook for about 2 hours, checking lamb every 30 minutes and basting as needed so exposed areas do not dry out. (TIP: USDA guidelines suggest a minimum internal temperature of 145°F for lamb. Temperatures during a braise will actually exceed that level, but when braised correctly, meats will remain cooked through without any loss of moisture.)Meanwhile, prepare herbed couscous: In a medium saucepan, heat olive oil on medium. Add onion and cook, stirring frequently, until soft. Stir in broth and raisins and bring to a boil. Add thyme, rosemary, marjoram and mint; immediately stir in couscous. Cover and remove from heat; let sit for 10 minutes, until liquid is absorbed. Fluff with a fork; stir in butter and parsley. Season with salt and pepper.Divide couscous among serving plates. Remove string from lamb shanks and arrange over top of couscous, dividing evenly. Remove and discard bay leaves. Top lamb with vegetable-sauce mixture, dividing evenly, and serve.