Preheat oven to 400F. Prepare muffin baking pan with liners.
In a large bowl combine dry ingredients: flour, cinnamon, baking powder, baking soda, and salt.
2 cups all-purpose flour, 3 tsp. cinnamon, 1 1/2 tsp. baking powder, 1 tsp. baking soda, 1/8 tsp. salt
In a large bowl mix wet ingredients: whisk eggs, add pumpkin puree, add oil, brown sugar and shredded apple.
3 eggs, 3/4 cup canola oil, 1 cup pumpkin puree, 3/4 cup brown sugar, 1 apple
Add dry ingredients to wet ingredients. Mix by spoon or spatula.
Pour the batter in each liner. Fill each liner fully.
Bake for 5 minutes at 400F. Lower the temperature to 350F while still keeping muffins in the oven and bake for 15 minutes.
Check if muffins are ready; inserted toothpick should come out clean. Remove muffins from oven and let them cool off on the baking rack.