Mix together cinnamon, flour, rolled oats, baking powder, salt and brown sugar.
Combine butter, treacle and vanilla in a separate bowl. Microwave on high power for 1 – 1 1/2 minutes, or until melted. Stir butter mixture into dry ingredients. Mix well.
Press half the mixture into a 34 by 18 cm microwave dish. Pour blueberries on top, then second measure of brown sugar. Sprinkle with remaining flour mix.
Microwave, uncovered, on medium power for 8 – 11 minutes, or until top is fairly dry.