1. Preheat oven to 375ºF. Line a 12-cup muffin tin with paper liners or mist with cooking spray.
2. In a large bowl, whisk flour, brown sugar, baking powder, baking soda, salt and cinnamon. Stir in oats. In a medium bowl, whisk yogurt, apple sauce, oil, egg and vanilla. Stir apples into yogurt mixture. Add yogurt mixture to flour mixture and stir until just moistened.
3. Divide batter among muffin cups. Bake until golden and a toothpick inserted into center of a muffin comes out clean, 22 to 24 minutes. Let cool in pan 5 minutes, then turn out muffins to rack to cool completely.
4. Combine cider or lemon juice and confectioners' sugar with a fork until smooth. Drizzle over cooled muffins and let stand until set, 15 to 20 minutes.
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