Put the diced chicken thigh, sweet potatoes and spring onions into the slow cooker pot.
Pour the jar of curry sauce into a small saucepan. Use the ½ cup of water to rinse out the remaining sauce in the jar, and add to the pan too. (Or you can also heat this up in a microwave).
Heat the curry sauce just to the boil. Then pour this over the chicken and veggies in the slow cooker pot. Stir well.
Cover and cook on High for 30 minutes.
After this time turn it down to Low and cook for 3 hours.
At this point, add the peas, season and lentils, if using.
Continue cooking on Low for a further 3 to 4 hours. Until the chicken and the sweet potatoes are cooked through.
Serve with rice, naan or a (tomato and cucumber) salad. And a dollop of cooling plain yoghurt.