Make the cupcakes: Preheat the oven to 350 degrees F. Line a 12-cup muffin pan with liners. Put the cocoa powder in a large bowl. Microwave the milk and water in a small microwave-safe bowl until steaming, 1 to 2 minutes; pour over the cocoa powder and whisk until smooth. Let cool slightly.
Whisk the flour, baking soda and salt in a small bowl. Whisk the sugar, vegetable oil, egg, vanilla and orange zest into the cocoa mixture, then whisk in the flour mixture.
Divide the batter among the prepared muffin cups, filling them three-quarters of the way. Bake until the tops of the cupcakes spring back when gently pressed, 20 to 25 minutes. Let cool 5 minutes in the pan, then remove to a rack to cool completely.
Make the ganache: Microwave the chocolate and heavy cream in a microwave-safe bowl in 30-second intervals, stirring, until melted, about 1 minute. Let sit until thickened but still pourable, 5 minutes. Spoon over the cupcakes, gently spreading to cover. Let set 10 minutes.
Meanwhile, make the meringue: Whisk the egg whites, sugar and cream of tartar in a large heatproof bowl set over a saucepan of simmering water (do not let the bowl touch the water). Cook, whisking, until the sugar dissolves, 2 to 3 minutes. Remove from the heat; beat with a mixer on medium-high speed until stiff glossy peaks form, 5 to 8 minutes. Tint with orange food coloring. Generously spread the meringue on the cupcakes and lightly brown with a kitchen torch.