In a 9" pie dish, combine leftover lamb with peas and carrots.
Top with leftover sauce and stir.
Spoon mashed potatoes on top of the lamb mixture. Use a spatula or back of spoon to gently spread the potatoes roughly evenly over the mixture.
Place pie dish on a foil-covered baking sheet to catch any drippings. Bake for 30 minutes until the potatoes begin to brown. Cool for 10 minutes before serving.
Notes
Need a lamb recipe? Start with tender Slow Cooker Lamb Shanks, and you will have plenty of leftover shredded lamb and sauce for this shepherd's pie: https://www.goglutenfreely.com/slow-cooker-lamb-shanks/10-Minute Sauce Recipe: