Preheat oven to 375°F. Lightly coat an 8-inch-square baking pan with cooking spray.

Place ½ cup dates in a medium heatproof bowl; add enough hot water to fully cover by ½ inch. Let stand at room temperature until the dates are slightly softened, about 20 minutes.

Meanwhile, combine 2 cups blueberries, 1 tablespoon water and ½ teaspoon vanilla in a small saucepan; bring to a boil over medium heat. Reduce heat to medium-low and simmer, stirring often, until the blueberries are mostly broken down and the sauce is slightly thickened, 6 to 8 minutes. Remove from heat and set aside.

Drain the dates and transfer to a food processor; pulse until finely chopped and sticky, about 10 pulses. With the processor running, slowly pour the remaining 7 tablespoons hot water through the chute, a few tablespoons at a time, until a semi-smooth paste forms, about 1 minute, stopping to scrape down sides as needed.

Add ½ cup coconut milk, 1 banana, 1 egg, 2 teaspoons coconut extract and the remaining 2 teaspoons vanilla to the food processor with the date mixture; process until smooth, about 1 minute.

In a large bowl, combine 2¼ cups oats, 1½ cups walnuts, ¾ cup coconut, 1 teaspoon baking powder, 1 teaspoon cinnamon and ¼ teaspoon salt. Add the date-banana mixture; stir until combined. Gently fold in the remaining 1 cup blueberries.

Spoon half of the oat mixture (about 3 cups) into the prepared pan; spread in an even layer to fully cover the bottom. Spread the blueberry sauce evenly over the oat mixture; top with remaining oat mixture, spreading evenly over the sauce.

Bake until just set in the center, 30 to 35 minutes. Let cool in the baking dish on a wire rack for 10 minutes before serving.