Preheat oven to 350 degrees. Grease a 9 x 5-inch loaf pan with cooking spray.
GINGERBREAD: In a medium bowl, whisk together flour, baking soda, ginger, cinnamon, allspice and salt; set aside.
In a small bowl, whisk together molasses, hot water and vanilla extract; set aside.
In a large bowl using an electric mixer, beat butter and brown sugar until light and fluffy. Beat in eggs one at a time.
Gradually add one third flour mixture, beating on low speed just until flour is incorporated. Add half the molasses mixture; once batter is smooth, add another third flour mixture. Add remaining molasses mixture beating until incorporated. Add remaining flour mixture, beating until smooth.
Pour batter into the prepared loaf pan. Bake 55-60 minutes, or until a toothpick inserted into the center of the loaf comes out clean.
Cool 10 minutes before removing from pan, then cool an additional 30 minutes.
CINNAMON ICING: In a small bowl, whisk together confectioners’ sugar, milk and cinnamon until smooth. Drizzle on top of gingerbread loaf.