Trim the outer leaves & stalk from the cauliflower. Divide into small florets, shred the leaves, wash & drain. Discard any discoloured cabbage leaves, cut cabbage into 1/4" slices, wash & drain. Drain the chestnuts & slice thinly. Drain the pineapple (if canned) & reserve the juice. Cut rings into eighths.
Cook the cauliflower & cabbage in boiling, salted water for 4 minutes. Drain well.
Blend cornstarch & sugar with the remaining ingredients. Place in a pan with the water chestnuts, pineapple chunks & juice. Bring to a boil & simmer for 3 minutes. Pour sauce over the cauliflower & cabbage. Stir well, cover & allow to cool.