Preheat char-grill pan or barbecue to medium heat. For coconut caramel sauce, spread sugar in a large deep-sided frying pan over medium heat and cook, shaking occasionally, until golden and melted (3-4 minutes). Add coconut milk (be careful, hot caramel will spit), stir to combine and cook until thick and syrupy (10-12 minutes). Set aside to cool slightly, then stir in butter and lime juice and set aside.
Brush bananas with oil and grill, turning occasionally, until golden and soft (10-15 minutes). Drizzle with coconut caramel sauce, scatter with coconut and peanuts and serve with lime wedges and extra sauce for dipping.