Step 1 Preheat oven to 190°C. Spray a large flameproof casserole dish with olive oil and place over medium–high heat on the stovetop. Add lamb and herbs to dish; cook, turning, for 5 minutes, or until lamb is browned all over.
Step 2 Add onion, garlic, cannellini beans, beef stock and passata to casserole dish; bring to the boil. Cover dish and transfer to oven. Cook for 1 hour, then turn lamb over and cook, covered, for another 50 minutes, or until lamb is tender, adding capsicums and peas for last 20 minutes.
Step 3 Meanwhile, microwave, boil or steam potato chunks until tender. Mash potato with skim milk, cover to keep warm and set aside.
Step 4 Serve lamb shanks and sauce with reserved mashed potato and a garnish of parsley.