Add the oats and eggnog to a large bowl. Stir to combine and let soak in the fridge for 30-60 minutes, or until the oats have softened.
Once the oats are soaked, preheat the oven to 425F. Grease every second cup in a 12-cup muffin tin so that 6 cups are greased and spaced out from each other.
Add the egg, brown sugar, oil and vanilla to the oat/eggnog mixture. Whisk to combine.
In a small bowl, whisk together the flour, baking powder, salt, nutmeg, cinnamon and ginger.
Add the dry ingredients to the wet mixture and stir to combine. Be careful not to over mix. Let the batter rest while you make the streusel topping.
To make the streusel, stir together the flour, brown sugar, nutmeg and cinnamon. Add the cubed butter and use your fingertips to work it into the dry ingredients until the mixture is crumbly. If the butter gets too warm as you work it in, just place the streusel in the fridge for 5-10 minutes.
Use a cookie scoop to spoon the batter into the prepared muffin tin, filling the 6 cups to the top.
Top each muffin with the streusel.
Bake at 425F for 5 minutes and then reduce the oven temperature to 350F and bake for another 14-16 minutes, or until a toothpick inserted into the center of a muffin comes out with just a few crumbs. Let cool for a few minutes in the pan and then transfer to a wire rack to cool completely.
Add the glaze ingredients to a small bowl and whisk until smooth. (Add more or less eggnog to get your desired consistency).
Drizzle the glaze over the cooled muffins and enjoy.