any suggestions on how to create a new meal with leftover roasted lamb?

Shepherd's Pie.

Lamb butty with gravy (French dip)

Or a salad:
Rocket, watercress, roasted red onions, roasted red peppers, balsamic glased roasted beetroot

If you want to bulk it up even more then you can have it with lentils or cous cous.

You can also add goats cheese or feta

Lamb rissoles or stir fry with garlic, chilli and ginger (and veggies of choice) - serve with noodles or rice.

Pasanda.
Kleftiko
Moussaka

Fajitas

Curry

If you have a selection of spices, this is heaven - Curried Leftovers.

I rarely have curry leaves and never have pumpkin/squash, for example but it still makes for a delicious, spicy stew.

Lamb hash