Boil, steam or microwave potato until just tender; drain.
Meanwhile, heat large non-stick frying pan; cook chorizo until crisp, remove from pan.
Place potato in same pan; cook, stirring gently, until browned lightly. Remove from pan.
Place combined oil, vinegar and sugar in same pan; bring to a boil. Boil uncovered, about 2
minutes or until dressing reduces slightly.
Combine potato and chorizo in large bowl with onion, spinach and tomato; drizzle with