Preheat oven to 350°F and line a muffin tin (or mini muffin pan). In a large bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt.
Add the Greek yogurt, eggs, oil or melted butter, maple syrup, milk, vanilla and mix until smooth. Stir until just combined, don’t over mix.
In a small bowl, mix together the melted butter, coconut sugar (or brown sugar), and cinnamon. Fill muffin liners about ¾ full, then add a small spoonful of the cinnamon mixture to each muffin and gently swirl with a toothpick or knife.
Bake for 20-25 minutes (for regular-size muffins) or 10-15 minutes (for mini muffins) or until golden and set. Let cool, then whisk together the Greek yogurt icing ingredients and drizzle over top before serving.
