Mix all of the sauce ingredients together in a large bowl.
Place the diced onion in the base of the slow cooker and top it with the chicken. Season with salt and pepper.
Put in the mango, pour over the sauce. Put the sliced red chilli on top.
Cook on high for 3 hours.
Make a paste from the cornflour and 2 tablespoons of cold water in a small bowl. Pour this into the slow cooker and mix well. This will thicken the sauce and also if the sauce happens to split due to the fresh fruit, it will bring it back together. Cook for another hour on high, then serve.
8 SmartPoints based on three servings. If you use 6 chicken breasts instead of 3 and the same amount of sauce (as there is plenty) then it will be 4 SmartPoints per serving.