Stir together the milk, water and pumpkin puree in a small bowl and set aside.
Melt the butter in a saucepan over medium heat. Add the oats and toast for about 2 to 3 minutes, stirring often, until fragrant.
Add the brown sugar, cinnamon, nutmeg and salt. Turn the heat to low and carefully pour in the liquids, stirring. Cover and cook on low heat without stirring for 5 minutes until tender. Remove from the heat. Serve immediately for a chunky texture, or stir in another 1/2 cup milk for a creamier body. The texture is intentionally chewy, not gloppy or soggy. Top with desired toppings (a drizzle of maple syrup is a must).