Preheat the oven to 180°C. Line a muffin tin with paper cases or put silicon muffin cases onto a baking sheet.
In a large bowl, combine the two flours, baking powder, bicarb and orange zest.
Add the orange juice, oil, eggs and vanilla. Combine until you get a smooth batter. You can add some flesh of the juiced oranges too (but not the pips).
Fill the muffin cases with the batter (almost to the top).
Peel the zested orange, then cut it into thin slices.
Place an orange slice on the top of each muffin.
Bake the muffins for 20 minutes, until golden.
Remove them from the oven and let them cool in the tin or silicon cases for 5 minutes, then transfer them to a wire-rack to cool completely.
Drizzle them with orange glaze or honey if you like.