In a small saucepan, heat the brown sugar, water, butter, salt and cinnamon over medium-high until bubbly. Add the nuts and stir to coat. Cook 3-5 minutes until very thick and syrupy, and the nuts are well-coated. Spread on baker's parchment in a single layer and allow to cool to room temperature.
Meanwhile, whisk together the frosting ingredients. Cover and set aside until ready to use (refrigerate if not using for more than an hour).
In a small saucepan, combine all oatmeal ingredients. Bring to a simmer then cook over medium-low heat, whisking frequently, until desired consistency is achieved, about 12 minutes.
Transfer oatmeal to a serving bowl. Top with frosting, then with nuts. Enjoy!