Melt the butter or coconut oil in a saucepan over medium heat. Add the oats and toast for about 2 to 3 minutes, stirring often, until fragrant.
Turn the heat to low and carefully pour in the water, milk, blueberries, brown sugar, cinnamon, allspice, salt, and vanilla extract, stirring. Bring to a simmer and cook for 5 to 7 minutes until thickened and the oats are tender, smashing the blueberries with the back of a large spoon as you stir. (Try to smash the majority of the berries to give the oatmeal its purple color.)
Remove from the heat. Top with desired toppings and serve.
