Here's what I would do it, depending on how much you have left...
(500g approx). I usually make my Shepherds Pie with Hidden Vegetables with 500g lamb mince as we never have that much roast lamb left, but Shepherds Pie started off as a leftovers recipe. And the grated vegetables (or roast ones if you have any left) stretch the meat a little further. 250g of leftover lamb with veggies could make a Shepherd's Pie for two.
Pasticcio (Cheat's Moussaka) is another option to stretch a fair amount. Dice the cold lamb and used instead of mince.
Stovetop Lamb Daube
Lamb Tagine - just cook on the stove like the Lamb Daube above
Veg Rich Kids & Toddler Lamb Curry - adults can eat this too!
Or a more traditional Indian Lamb Curry. Again don't cook this in the slow cooker. Skip browning the meat and start with making the sauce, adding the lamb to simmer with all the ingredients for 30 minutes
I made a tasty Roast Lamb & Couscous Salad last week when the weather was more springlike!
Or a Spicy Korean Salad
More warming options are Lamb Dhansak or Lamb Korma, where veggies can be added if you don't have a lot of lamb. The Korma works well with cauliflower.
Not much at all
Soup is probably the best bet if you only have a tiny bit of lamb left. Mulligatawny Soup was recommended to me buy one of my soup buying customers at the Country Market. It is deliciously warming on a snowy day in March such as this. 100g of lamb makes 5-6 bowls so a smaller quantity of lamb would still make a hearty soup for 1 or 2 people. And any leftover veggies could also find a good home in there.
Scotch Broth is another soup option.