Preheat oven to 350°F. Spray a 8.5 x 4.5” loaf pan with baking spray and line with parchment, leaving an overhang so the cake can be easily lifted from the pan once baked and cooled.
In a large bowl, whisk together 2 cups flour, sugar, baking powder, and salt. Add eggs, oil, lemon zest, vanilla extract, and buttermilk. Mix well until all dry ingredients are incorporated.
In a small bowl, toss blueberries with 2 tablespoons of flour until all are evenly coated. Fold blueberries into cake batter.
Pour into the prepared pan and top with crumble. Bake for 55 to 60 minutes, or until center has set and a wooden pick inserted into the center of the cake comes out clean.
Transfer pan to a wire rack to cool completely.