Dry shanks; coat in flour, shake off excess.
Keep the lid open and select SEAR program. Add 1 tablespoon of oil in the cooking pot and brown the shanks two at a time (about 12-15 minutes) and set aside; repeat with the remaining two shanks. Remove shanks; set aside.
Keep the lid open and select SEAR program. Add remaining 1 tablespoon oil, onions, carrots, and garlic. Cook and stir for about 10 minutes or until softened.
Add wine, stock, tomatoes, rosemary, and lemon zest. Return all lamb shanks to the cooking pot. Close and lock the lid. Select PRESSURE COOK program Level 7 and Timer 25 minutes.
Once the timer beeps 3 times to indicate the end of cooking, manually release pressure by pressing on the steam release button for about 5 seconds . The steam release process will take about 4 to 5 minutes. Meat should be very tender and almost falling off the bone.
Season with salt and pepper to taste. Serve lamb with vegetables and pan sauce.