Preheat the oven to 350 degrees F.
Line muffin tins with cupcake liners.
Sift together the flour, baking soda, salt, nutmeg, and cinnamon.
In a stand mixer combine the sugar, oil, water, pumpkin, vanilla extract, and eggs until thoroughly combined
Slowly add the flour mixture. Mix until combined.
Mix the brown sugar and cinnamon.
For the streusel topping: in a small bowl mix together the oats, flour, brown sugar, cinnamon, and nutmeg. Mix in the butter with your hands until the mixture is crumbly.
Fill muffin cups 1/4 way full then sprinkle with brown sugar mixture. Then cover with 1/4 more filling so that muffins are 2/3 way full.
Top muffins with streusel topping
Bake muffins for 20 minutes or until a toothpick inserted comes out with minimal crumbs.
Cool muffins on wire rack.
While muffins are cooling combine the glaze ingredients. Drizzle over muffins once cooled.