Add the lamb, chopped turnip, and sliced or quartered mushrooms to a slow cooker or the inner pot of an Instant Pot.

Pour in the beef broth, then add the onion powder, garlic paste, and a good pinch of salt and pepper. Stir well.

Cover and cook on High for 3 hours or Low for 6 hours (use the Slow Cook setting if you're using an Instant Pot), until the lamb is fork-tender and the turnips are cooked through.

Taste the broth and adjust the seasoning. Use a slotted spoon to transfer the lamb and vegetables to a serving dish, then spoon some of the cooking liquid over the top. For a slightly thicker sauce, whisk a pinch of xanthan gum into the remaining liquid before spooning it over.

Garnish with chopped fresh flat-leaf parsley and serve.