Step 1Pat lamb shanks dry with paper towel and salt liberally on all sides. Heat oil over medium heat in large cast-iron Dutch oven. When hot enough that meat instantly sizzles when added to pan, brown shanks on all sides. You may need to do this in two stages, depending on size of pan. As shanks are browned, remove to plate and keep warm. Do not brown shanks too quickly or they will be dry. It should take about 15 minutes.
Step 2When shanks are browned and have been removed to plate, drain all but film of fat from pan. Add carrots, celery, onion and bell pepper and cook, stirring, until vegetables begin to soften, about 10 minutes.
Step 3Add garlic and cook, stirring, until garlic becomes very fragrant, about 5 minutes. Add tomato paste and cook, stirring, until you see dark streaks across bottom of pan where paste is browning, about 5 minutes. Add wine and stir to combine well.
Step 4Place shanks on top of vegetables. Cover with sheet of aluminum foil to fit snugly against sides of pan. Cover tightly with lid and bake at 350 degrees 45 minutes.
Step 5Remove lid and foil and add olives and good grinding of black pepper. Stir to mix well. Turn shanks and check level of liquid. Wine should just cover vegetables and bottom of shanks. Add more wine or water if necessary. Return to oven and bake until lamb is tender enough to fall off bone, another 45 to 60 minutes.
Step 6Remove from oven, turn lamb again and add rosemary. Cover and set aside 5 to 10 minutes. Season to taste with salt. Chop together lemon zest and parsley. Serve shanks with some sauce and with lemon-parsley combination sprinkled over top.