1. Preheat a grill to medium-high heat.
2. Coat the corn evenly with the oil. Grill the corn, turning so that it cooks evenly and grill marks form, 10 to 12 minutes.
3. Mix together the mayonnaise, Sriracha, lime juice and chilli powder until smooth.
4. Coat the corn with the mayonnaise mixture. Sprinkle with the chopped coriander, if using, and garnish with more chilli powder for extra heat.