Bring the water and salt to a boil in a 2-quart / 1.9 L saucepan over high heat.
Stir in the steel-cut oats. Reduce heat to low, cover partway, and simmer for 25 to 30 minutes, stirring every 5 minutes or so, until the oats are tender and most of the water is absorbed.
Pour in the milk during the last 5 minutes of cooking and stir. Oats can turn gluey if you walk away too long here, so keep an eye on the pot and add a splash more milk or water if it looks too thick.
Remove from heat once the oats are creamy but still hold some chew, not mushy. Stir in the cinnamon.
Divide the oatmeal between 4 bowls.
Swirl 1 tablespoon of almond butter into each bowl while the oats are still hot, so it melts slightly.
Top with sliced banana and a drizzle of maple syrup if using.
Scatter chopped nuts over top for crunch and serve right away.