Preheat the oven to 200 C, Fan 180, Gas 6. Slice the sweet potatoes into 1/3 inch thick slices. Brush lightly with olive oil and place in the bottom of a ceramic roasting dish.
Brown the chicken pieces in olive oil, then place the legs only on top of the sweet potatoes and bake for 25 minutes.
Meanwhile make the olive sauce by blending all the in sauce ingredients in a food processor using the pulse setting until fairly fine but not a puree.
After 25 minutes remove the dish from the oven, turn the legs over and add the breast pieces. Return to the oven and cook for a further 25 minutes,
Remove from the oven, pour over the sauce and return to the oven until the chicken is cooked. Check by inserting a knife into the thickest part of the breast and ensuring the fluid runs clear.