In a medium saucepan over high heat, bring milk to a boil. Stir in oats and 1/2 tsp cinnamon, reduce heat to low, and simmer until oats are tender and creamy, 5 minutes.
Serve oatmeal in a bowl drizzled with icing and sprinkled with remaining 1/2 tsp cinnamon.
Icing
In a small bowl, whisk together remaining 2 tsp. milk and powdered sugar.