I use an overnight marinade for my roast. There are several on this site to pick from. I cook per recipe #600948 High Altitude Lamb. I have all the seasonings in the marinade that are listed in this, so I only add the slivers of garlic. Reserve the juices and freeze for use in the stew. After a few meals of the roast, I throw the leftover in the freezer until I want to make some stew.
In a crock pot, combine all ingredients. Amount of vegetables can be adjusted. I state 4 cups of water, I add enough water to slightly cover the ingredients. Cover & cook on high for a few hours then turn on low and cook for about 8-10 more hours. I find with stew, the longer you cook it the thicker it gets. (If you prefer a thick stew, you can flour your lamb prior to placing in crock pot too.) All ingredients are adjustable to your taste.
Prep time and cooking time do not include the cooking of the roast.