Make the puddings: Sift the sugar, cornstarch, cocoa powder and salt through a fine-mesh sieve into a medium saucepan. Add the coconut milk and whisk occasionally over high heat until the mixture comes to a bubble and thickens, about 5 minutes.
Pour the mixture through the sieve set over a medium heatproof bowl to remove any lumps. While the pudding mixture is still hot, add the chocolate and whisk until smooth. Divide the pudding mixture among four 1-cup ramekins or serving dishes. Refrigerate for at least 4 hours, preferably overnight.
Make the topping: Combine the cereal, coconut and sugar in a large nonstick skillet over high heat. Cook, stirring, until the coconut is toasted and fragrant, about 2 minutes. Transfer to a small bowl. Add the salt, toss to combine and let cool slightly.
To serve, cut each passion fruit in half and scoop the flesh onto the puddings. Garnish each pudding with a hearty spoonful of the cereal-coconut topping and serve.