Preheat your oven to 350° F.
Heat a pan over medium heat. Combine lemon juice and 3 tablespoons of brown sugar. Once dissolved, add diced apples and sauté for 5-7 minutes to create the filling. Set aside.
Add the base ingredients to a small-sized mixing bowl and stir to combine. The mixture may seem a bit dry, but it will come together in the next step.
Line a 9x9-inch square pan with parchment paper. Press the mixture into the pan with your hands, flattening it to make an even layer.
Pour sautéed apples over base layer and spread evenly.
In a small mixing bowl, create a crumb topping by combining gluten-free flour, dairy-free butter, brown sugar, and cinnamon.
Sprinkle the crumb topping evenly over the apples.
Bake for 40 minutes, until golden brown.
Allow baked bars to cool slightly, about 10-15 minutes, before slicing into nine squares.
Enjoy for breakfast or brunch, or serve as a cozy fall dessert.