Peel the bananas and lay them in a snug-fitting heatproof dish. Finely grate the orange zest and put aside, then halve and squeeze over the juice of 1½ oranges.
Drizzle with the honey and sprinkle over 2 teaspoons of the cinnamon, then roast in the oven for around 20 minutes, or until golden and soft, then set aside to cool.
Place the bananas and their syrup in a blender, then blitz with the milk and yoghurt.
Add in a handful of the zest, the juice of the remaining orange half, a pinch of sea salt and the rest of the cinnamon, then churn in an ice-cream machine. If you don’t have one, freeze the mixture in a suitable container for about 3 hours; every hour, take it out, whip with a whisk, then return to the freezer.
Serve in bowls with a scattering of orange zest and a fine grating of dark chocolate.