1. Preheat the oven to 375 and butter a 2-qt baking dish. Make the filling: toss the blueberries, sugar, flour, lemon juice, and salt in a medium bowl. Transfer to the prepared baking dish.
2. Make the topping: combine the brown sugar, flour, oats, nuts, lemon zest, cinnamon and salt in a separate bowl. Using your fingers or a pastry blender, work the butter into the flour mixture until coarse crumbs form. Scatter the topping over the blueberry mixture.
3. Set the dish on a baking sheet and bake until the topping is golden brown and the filling is bubbling, 45-50 minutes. Let cool SLIGHTLY before serving.