Preheat oven to 350°F (175°C). Line a small loaf pan (6×3-inch) with parchment paper.
Mix wet ingredients: Whisk together pumpkin purée, egg, oil, yogurt, sugars, and vanilla.
Add dry ingredients: Stir in flour, baking soda, salt, and spices. Mix gently until just combined.
Make the swirl: In a small bowl, combine brown sugar and cinnamon.
Assemble: Pour half the batter into the pan, sprinkle the cinnamon sugar, then add the remaining batter. Gently swirl with a knife in a figure-8 motion.
Bake: 40–45 minutes, or until a toothpick comes out clean.
Cool: Let rest 15 minutes in the pan, then move to a wire rack. Slice and enjoy warm.