In a medium saucepan, combine 1 cup of old-fashioned rolled oats, 1 3/4 cups of water, and a pinch of kosher salt. Bring the mixture to a gentle boil over medium-high heat.
Reduce the heat to low and simmer the oatmeal, stirring occasionally, for about 5-7 minutes, or until the oats have absorbed most of the water and the mixture has thickened.
Stir in 2 tablespoons of light brown sugar and 1/2 teaspoon of ground cinnamon until they are fully incorporated into the oatmeal.
Mash one large ripe banana with a fork in a small bowl until smooth, then fold it completely into the cooked oatmeal until the mixture is uniform in color.
Gently fold in 1/2 cup of fresh raspberries, being careful not to overmix to prevent them from breaking down completely.
Remove the saucepan from the heat and divide the oatmeal evenly between two bowls. Serve immediately, drizzling with 1 tablespoon of whole milk per bowl if desired.