Preheat the oven to 375°F (190°C). Line a 9 x 13 inch (23 x 33 cm) baking pan with parchment paper, cutting it large enough so the sides come all the way up the sides of the pan. The overhanging paper will make it easy to pull the bars from the pan after baking.
In a large bowl, whisk together the flours, oats, sugar, baking powder, salt, and lemon zest. Transfer to the bowl of a food processor. Add the cubed butter and pulse 15 times. Scrape down the bowl and stir the mixture using a spatula, then pulse 15 times. Add the egg, pulse 15 times, then scrape down the bowl and stir the mixture again. Process for a few seconds until the dough is crumbly.
Spoon half of the crumb mixture into the prepared parchment-lined baking pan. Using your hands, press the mixture down firmly to create the bottom crust.
In a second large bowl, stir together the blueberry layer ingredients. Sprinkle the blueberry mixture evenly over the crust. Spread the remaining crumb mixture over the blueberry layer.
Bake for 45 minutes, or until top is slightly brown and blueberries are bubbly around the edges. Cool completely before cutting into bars.