Gently toss the pieces with oil and add a bit of salt and pepper. Try to make sure the oil is well distributed.
Lay the kumara onto baking paper in shallow gastro and roast in the oven
once the kumara starts to take colour on 1 side (after about 20 - 25 mins) then carefully turn cook a further 15-20 mins until a little coloured and kumara is cooked through.
Cool and store in fridge
Cut spring onions reasonable fine and store
Sauce prep
Add all sauce ingredients together and blend in a food processor till smooth.
On site
Mix half of all ingredients together in a large bowl. Mix further as required. Best served within 30 mins or so