Chop 1 yellow onion, 2 large carrots (peeling optional) and 3-4 stalks celery into ~1-2” pieces.
Season lamb roast on all sides with ~3T Italian seasoning and a generous amount of salt & pepper.
Place chopped veggies, seasoned lamb and 28oz diced tomatoes in a slow cooker.
Cook on low for 6-8 hours or high for 4-6 hours.
Remove roast from slow cooker and slice thinly, against the grain.