For the syrup: Whisk together the maple syrup, cinnamon, salt and cayenne in a small saucepan. Bring to a simmer over medium-low heat and whisk until the cinnamon is dissolved, about 1 minute. Remove from the heat and stir in the orange zest. Cover and keep warm.
For the waffles: Preheat a waffle maker to medium-high. Preheat the oven to 95°C. Whisk together the flour, baking powder, baking soda, chipotle powder, cinnamon and salt in a medium bowl. Whisk together the buttermilk, pumpkin puree, oil, sugar, egg and white. Pour the buttermilk mixture into the flour mixture and gently stir until just incorporated (it's ok if there are lumps).
Lightly brush the top and bottom of the waffle iron with oil. Fill each section about three-quarters of the way full (there should still be some waffle iron showing). Close and cook until the waffles are golden brown and slightly crisp, 6 to 10 minutes. Keep the waffles warm in the oven or covered with foil on a plate while you cook the remaining batter.
Serve the waffles with butter, drizzle with the orange syrup and sprinkle with the pepitas.