Preheat oven to 375 degrees. Grease and flour a 9 x 13-inch baking pan.
COFFEE CAKE: In a large mixing bowl, whisk together flour, sugar and baking powder. Make a “well” in the center of the flour mixture. Add melted butter, milk, eggs, vanilla, lemon zest and juice. Beat until combined. Gently fold in blueberries with a spoon or spatula. Pour batter into a prepared baking pan, spreading coffee cake batter evenly.
CRUMB TOPPING: In a medium bowl, whisk together flour, brown sugar and cinnamon. With a pastry cutter or fork, cut butter into the flour mixture until it resembles small peas. Sprinkle topping over the coffee cake batter and bake for 30-35 minutes.