I've adapted this lamb curry recipe and have found it works well in the slow cooker and also in a pressure cooker. It's really tasty, not too hot, and made with simple ingredients. You can use various curry pastes but korma or massaman work for me.
The grated sweet potato will melt into the sauce and help to thicken it. If your slow or pressure cooker has a saute function, you can use it to complete step 3 at the same time as you are cooking the meat in the frypan (step 2). Half korma, half massaman curry paste works well if you don't want it too hot.