Roast the eggplant in the oven at 400 for about 30-40 minutes, until soft.
In a wide pan, cook the lamb over medium-high heat until completely cooked through and any liquid has evaporated fully. The original specifies well-cooked mince and this matters for the texture of the filling. Drain any excess fat.
Add the finely minced onion to the pan with the lamb and cook together over medium heat for 10 to 12 minutes until the onion is completely soft and beginning to turn golden. Add the dried ginger and ground garlic and cook for a further 3 minutes.
If using saffron, grind the threads to a powder using a pestle and mortar. Steep in 2 tablespoons of rosewater for 5 minutes until the liquid turns deep amber-gold. Add to the lamb mixture along with the eggplant pulp. Stir well to combine everything thoroughly. Season with salt. Allow to cool completely before filling the samosas.