Toast walnuts. Set aside. Place half the banana in a small pot and use a wooden spoon to roughly mash.
Add milk, water, pinch salt, maple syrup, cinnamon, and nutmeg to pan and bring to a simmer over medium heat.
Stir in oats and cook for approx. 1 – 2 min., stirring constantly.
Remove from heat, stir in vanilla extract, and transfer to a serving bowl.
Slice remaining banana half and garnish porridge along with toasted walnuts, raisins and a drizzle of honey.