Grease an 8x1-1/2-inch round baking pan and set aside.
In a medium mixing bowl, stir together flour, rolled oats, sugar, baking powder, and salt. In a small mixing bowl, stir together egg, milk, and cooking oil. Add all at once to dry mixture. Stir until just moistened (batter should be lumpy). Fold in blueberries. Spoon batter into the prepared round baking pan.
Bake the coffee cake in a 400 degree F oven for 20 to 25 minutes or until the cake is golden and a toothpick inserted near center comes out clean.
Cool in pan on a wire rack for 5 to 10 minutes. Drizzle warm cake with Powdered Sugar Icing, if you like. Serve warm. Makes 8 servings.
In a small bowl stir together powdered sugar, 2 teaspoons milk, and the vanilla. Stir in enough additional milk, 1 teaspoon at a time, to make icing a drizzling consistency.