2tablespoonscoarse sugar, such as demerara or raw sugar
Preheat the oven to 350 F. Lightly spray or wipe the bottom and sides of a 8 X 8-inch glass baking pan with oil or cooking spray. (You may use metal, but the baking time will vary.)
Put the oats into a blender and grind until they are fine. Stir a couple of times to make sure that they're uniformly ground.
Mix the oat flour with the other dry ingredients. Stir in 1/4 cup of the blueberries.
Put the remaining cup blueberries into a blender or food processor with the water. Pulse (quickly turn on and off) to coarsely chop the blueberries, but do not completely puree. Make a well in the center of the dry ingredients and pour in blueberry mixture and other wet ingredients. Stir until moistened and completely combined, but don't over-mix. Pour into the prepared pan (batter will be thick). Mix together the sugar and cinnamon topping, and sprinkle it over the top.
Bake for 25-35 minutes, until a toothpick inserted in the middle comes out clean. Allow to cool for at least 15 minutes. Eat and celebrate!
For a slightly lighter--but not fat-free--cake, add one tablespoon canola oil with the wet ingredients. This adds 14 calories and 1.5 grams of fat per serving.