Combine the Lucky Charms cereal and milk in a bowl and allow the cereal to steep in the milk for around 30 minutes. Strain the cereal from the milk and set the milk aside
Preheat the oven to 350 degrees and grease 2 donut pans with nonstick cooking spray.
Stir together the flour, baking powder, salt, and sugar in a large bowl. Add the oil, vanilla, eggs, and cereal milk. Whisk until fully combined
Transfer the batter to a piping bag and pipe it into the donut pans. Bake for 12 to 15 minutes, until the donut bounces back when pressed with your finger.
Allow the donuts to cool in the pan for 5 minutes, then transfer to a wire cooling rack to cool completely.
Once the donuts have cooled down, place the mini marshmallows in a microwave safe bowl and heat in the microwave for 30 seconds to melt. Then, beat together the butter, marshmallow creme, vanilla extract, and green food coloring until smooth.
Add the powdered sugar and one tablespoon of cereal milk and beat to combine. Add more milk, as needed, until the desired consistency is reached.
Dip each donut in the icing, then top with more Lucky Charms before serving.