Preheat oven to 350°F. Lightly spray one 8″ X 4″ inch loaf pan or 4 mini pans. Mix together 1/2 cup brown sugar and 2 teaspoons cinnamon, set aside.
In another bowl combine flour, baking powder, salt, granulated sugar and remaining teaspoon of cinnamon. Combine egg, milk, oil and vanilla. Add to flour mixture. Stir until just moistened.
Place half the batter into the pan and a little more than half of the cinnamon-sugar mixture. Then pour the rest of the batter on top. Sprinkle the remaining cinnamon-sugar mixture. Draw a knife through batter to swirl the mixture.
Bake in preheated oven for 50 to 60 minutes (smaller pans check after 20 minutes), or until a toothpick inserted into center of the loaf comes out clean. Allow to cool.
Mix together the confectioners' sugar, milk, butter, vanilla and salt until creamy. Add more milk if needed. Then drizzle it on top of the bread.