01 - Preheat oven to 350°F. Grease and line a 9x5-inch loaf pan with parchment paper.
02 - In a large bowl, whisk together gluten-free flour, sugar, cinnamon, baking powder, baking soda, and salt.
03 - In a separate bowl, whisk eggs, applesauce, oil, and vanilla until smooth.
04 - Add wet ingredients to dry ingredients and stir until just combined, avoiding overmixing.
05 - Mix brown sugar and cinnamon in a small bowl.
06 - Pour half of the batter into the pan. Sprinkle half of the cinnamon swirl mixture over it. Add remaining batter and top with remaining swirl mixture. Gently swirl with a knife.
07 - Sprinkle chopped nuts on top if using.
08 - Bake for 38 to 42 minutes, or until a toothpick inserted in the center comes out clean.
09 - Cool in pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.