Heat the oven to 350°F and line a 12-cup muffin pan.
Whisk the flours, baking powder, baking soda, salt, and cinnamon in a bowl.
Whisk melted coconut oil, yogurt, brown sugar, eggs, and vanilla in a second bowl.
Fold the wet mixture into the dry ingredients just until combined, then fold in the diced apples.
Divide batter among the cups. Mix granulated sugar and cinnamon and sprinkle over each muffin.
Bake 22 to 25 minutes, until domed and a toothpick comes out with moist crumbs. Cool briefly before serving.
Notes
Model-authored fallback: quantities and method were reconstructed from the source identity and accessible WordPress recipe signals; verify the center is baked through.