Cut cucumber lengthwise in quarters. Slice each quarter into 1/4-inch slices.
Peel pineapple and cut into quarters. Remove core. Cut each quarter in half and slice into 1/2-inch slices.
Cut red onion in half and thinly slice each half.
Remove thick stalks from watercress and reserve leaves.
Combine cucumber, pineapple, onion and watercress leaves in a bowl. in another bowl, combine lemon juice, soy sauce, sugar and chili sauce.
Pour over salad and toss together.
Serve on a platter.