Preheat oven to 400 degrees. Prepare a muffin tin with paper liners.
In a medium bowl, combine flour, baking powder, baking soda, salt, sugar, and walnuts.
In a small bowl, whisk together eggs, yogurt, milk, oil, orange zest, and chopped rosemary.
Add dry mixture to wet mixture and mix until just combined; do not overmix.
Using an ice cream scoop, scoop batter into liners. Bake for 16-18 minutes until tops are slightly golden and firm, and a toothpick inserted in the center comes out clean.
Cool on a baking rack for about 30 minutes or until completely cooled. Spoon icing over top and decorate with a small sprig of rosemary.