Heat a large frying pan over medium-high heat. Brush corn with 1 tbs oil and cook, turning, for 12 minutes or until tender and charred. Set aside to cool slightly, then using a small knife, cut kernels from cob. Discard cob.
Meanwhile, heat 1 Tbsp remaining oil in a saucepan over medium heat. Cook couscous, stirring, for 1 minute or until light golden. Add 2 cups boiling water. Reduce heat to low and simmer, covered, for 10 minutes or until liquid has been absorbed and couscous is tender.
Heat remaining oil in frying pan over medium-high heat. Cook chorizo, turning, for 5 minutes or until golden and crisp. Using tongs, transfer chorizo to a plate lined with paper towel. Transfer oil from pan to a small heatproof jug. Whisk lime juice into chorizo oil, then season.
Combine couscous, chorizo, corn, onion, tomato and parsley on a platter. Drizzle with chorizo oil dressing, top with extra parsley leaves and serve.