Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine the huckleberries, ½ cup of sugar, and lemon juice. Gently toss the mixture to coat the huckleberries and set aside.
In another bowl, mix together the flour, oats, the remaining ½ cup of sugar, ground cinnamon, and salt.
Pour in the melted butter and stir until the mixture is crumbly and evenly combined.
Spread the huckleberry mixture evenly in the bottom of the 9x13-inch baking dish.
Sprinkle the oat topping over the huckleberries, spreading it out evenly.
Bake in the preheated oven for 30-35 minutes or until the top is golden brown and the filling is bubbly.
Remove from the oven and let it cool for a few minutes before serving.
Serve warm or at room temperature with a scoop of vanilla ice cream or whipped cream for an extra treat.