Turned out Beautifully
I really enjoyed this. It was my first go at cooking lamb, and I'm certain I'll make it again. This was delicious. The eggplant melted into the sauce, and the other veggies held their shape. It tasted very rich and satisfying without needing cheese or cream or anything like that. I had regular eggplant, so I did the extra salting step before cooking.
I could not find sumac anywhere, even at my bulk spice store. So, I subbed chicken stock for water to up the flavor, and right before serving, I squeezed in a small lemon's worth of juice. I'd love to try this with the spice next time if I can find it.