Preheat the oven to 425°F and grease 12 standard size muffin tins and line with cupcake liners.
In a large bowl, combine the vegetable oil, brown sugar, eggs, greek yogurt, milk, vanilla extract, shredded carrots and shredded coconut. Whisk until combined.
Add the flour, baking powder, salt, and cinnamon to the wet ingredients and whisk until just combined and no streaks of flour remain. Do not overmix the batter. If using, add the raisins and fold to combine.
Scoop batter into prepared muffin tins, filling about 3/4 of the way. You can use a large cookie scoop or a 1/4 cup measure to keep things consistent.
Bake for 5 minutes at 425°F, then turn the oven down to 375°F and bake for an additional 15 minutes, until muffins are golden brown and spring back to the touch.
Make the glaze while the muffins bake. Combine all the ingredients for the icing in a bowl and mix together until smooth and creamy.
Remove the muffins from the oven and let cool completely. Microwave the glaze for 30 seconds to thin it out and then spoon over each muffin. If desired, top with chopped walnuts! Enjoy!