In a large bowl, combine rosemary, thyme, salt, and pepper. Add lamb shanks and rub with herb mixture.
Heat 2 tablespoons olive oil in a large (8-quart) Dutch oven over medium-high heat. Add 3 or 4 shanks and brown each on both sides, about 7 to 10 minutes per side. Transfer to another bowl. Repeat with remaining shanks, adding more oil as needed.
Skim excess fat from pan and discard. Reduce heat to medium and add carrots and onions. Cover and cook (stirring occasionally to scrape up browned bits) until vegetables have softened, about 5 minutes. Add wine; increase heat to high and boil uncovered until liquid is reduced by half, about 4 minutes. Add stock, garlic, and lemon peel. Add shanks and bring to a boil. Cover pan, transfer to oven, and bake 1 hour. Rearrange shanks so any exposed meat is immersed in broth. Bake shanks an additional 1 to 11/2 hours, or until meat is fork tender. Using tongs, transfer shanks to a platter; cover and keep warm.
Skim excess fat from broth and discard. Unwrap garlic and remove cloves from skins with a small, sharp knife. Whisk garlic into broth and return to a boil. Remove vegetables; season with salt and pepper, and arrange on platter with lamb. Boil broth 10 to 15 minutes, until slightly thickened; pour over shanks.
Combine all gremolata ingredients in a small bowl. Garnish lamb with it and serve.