Preheat the oven to 350°F.
Spread the pecans evenly onto a baking sheet.
Place the baking sheet in the preheated oven and toast the pecans for 7 to 10 minutes, or until fragrant.
Shake the baking sheet halfway through the baking time to ensure even toasting.
Remove the pecans from the oven and allow them to cool completely.
In a large saucepan over medium heat, combine the water and whole milk.
Bring the water and milk mixture to a gentle simmer.
In a separate large saucepot, melt the butter over medium heat until it just begins to foam.
Add the steel cut oats to the melted butter.
Stir the oats for approximately 2 1/2 minutes, or until they are lightly golden and fragrant.
Once the milk mixture is simmering, add the toasted oats to the saucepan.
Reduce the heat to medium-low.
Simmer the oats uncovered, without stirring, for approximately 20 minutes, or until the mixture thickens and resembles gravy.
Add the salt and vanilla extract.
Stir lightly to incorporate.
Continue simmering the oatmeal, stirring occasionally, for 7 to 10 minutes, or until most of the liquid has been absorbed and the oatmeal is thick and creamy.
Turn off the heat.
Allow the oatmeal to stand for 5 minutes before serving.
Spoon the oatmeal evenly into 4 serving bowls.
Top each serving with 1 tsp dark brown sugar, a dash of cinnamon, 1 tbsp chopped toasted pecans, and half of a sliced banana.
Serve warm.