Preheat oven to 350 degrees F.
To make the crumb topping, add the flour, brown sugar, cinnamon and salt in a medium bowl. Mix together. Add in the cold butter and cut into the flour mixture using a pastry cutter or fork until the butter is broken down into small pieces. Place the crumb mixture in the refrigerator while you prepare the cake batter.
In a medium mixing bowl, add the flour, salt, baking soda, and baking powder together. Set aside.
In a separate large mixing bowl, add the sugar and lemon zest. Using your hands, rub the zest into the sugar to release the oils. Add in the eggs and beat together until fully combined. Add the oil, milk, vanilla extract, lemon juice, and Greek yogurt. Mix together.
Pour the dry ingredients into the wet and stir until just combined.
Toss the blueberries in 1 Tablespoon of flour in a small bowl. This will help prevent the blueberries from sinking to the bottom of the cake. Add the blueberries to the cake batter and fold in.
Pour the batter into an 8x8 metal greased baking dish and spread out evenly. Sprinkle the crumb topping evenly on top.
Bake for 35-40 minutes or until the cake has set and a toothpick comes out clean.