Preheat an oven. Coat the bottom of the baking dish or cast iron pan with nonstick baking spray. Place frozen blueberries, sugar, all-purpose flour, lemon zest, fresh lemon juice, ground cinnamon, and Kosher salt directly into the dish, then stir well.
In a medium bowl, whisk together flour, rolled oats, brown sugar, ground cinnamon, and Kosher salt. Add melted butter, then stir until coarse crumbs form. Sprinkle over the top of the blueberry filling.
Bake until the topping is golden brown and the blueberries are bubbling. If you serve the blueberry crisp immediately. For a firmer texture, let it sit until mostly or fully cool. Top with generous scoops of coffee or vanilla ice cream.