For variety, I often use an electric slow cooker (or a gas or coal fired potjie...i.e. a cast iron pot or "witches cauldron") to slow cook lamb and beef curries....they come out a treat!

I also use a slow cooker to precook lamb or beef, for a couple of hours. The meat turns out just fine.
Ray, maybe try using Dipuraja's precooked meat recipe here:
https://curry-recipes.co.uk/curry/index.php?topic=4356.0I've tried it with chicken (out of interest) and it turned out really tasty. Though, I admit, I didn't cook it for anywhere near the suggested 35-40 minutes (probably only for 15 minutes or so). I haven't tried his recipe for lamb (or beef) yet, but I imagine it will come out really tasty and tender if you slow cook it for an hour or two.....