Preheat oven to 350 degrees Fahrenheit. Line a muffin tin with 12 cupcake liners.

In a large bowl, stir together the almond meal, brown sugar, baking powder, cinnamon, and salt.

Make a well in the center of the dry ingredients and pour in the eggs, oil, and vanilla extract. Mix with the dry ingredients until smooth. Mix in the chopped apple and chopped walnuts last.

Divide batter evenly into cupcake liners, filling each almost to the top. Bake muffins for about 25 minutes, or until the muffins are golden brown and an inserted toothpick comes out clean. Let muffins cool before glazing.

In a small bowl, whisk together all the glaze ingredients until mixture is smooth and is a pourable consistency.

Drizzle glaze in zigzag pattern over each muffin.