Rinse the oranges, pat dry, finely grate the zest and squeeze the juice into a saucepan. Slice the vanilla bean in half lengthwise and add to the saucepan. Dice the pumpkin flesh and simmer with the orange juice and vanilla bean until softened. Remove the vanilla bean and puree the pumpkin with an immersion blender until smooth.
Preheat the oven to 200°C (approximately 400°F). Line a muffin tin with paper baking cups.
Stir the sugar, honey, eggs and buttermilk into the pumpkin puree. Finely chop the pumpkin seeds in a food processor and mix with the orange zest, flour, baking powder, cinnamon and cocoa powder. Stir the pumpkin mixture into the flour mixture and mix until smooth. Finely chop the chocolate and fold into the batter. Spoon the batter into the prepared muffin tin and bake for 20 minutes, until a toothpick inserted comes out clean. Remove from the oven and cool on a wire rack.