Prepare. Preheat your oven to 350° F/175C. Also, prep your baking pan for nonstick. Parchment paper should work in this recipe.
Base. To make the base layer, in a large mixing bowl, use a whisk to combine together the flour, sugar, baking powder, and salt. Then whisk in the oil and water, mixing until it forms a crumbly mixture. Transfer the ingredients into your prepared pan and press the ingredients into an even layer covering the bottom of the pan.
Crumble. In a clean bowl, use a clean whisk to combine together the flour, brown sugar, ground cinnamon and salt. Once combined, add the oil and water to the bowl and mix until small crumbles form. You want there to be 'pea-sized' crumbles. You can use your hands if needed to make the crumbles once the ingredients have been 'just combined'.
Filling. In another clean bowl, toss together your sliced apples with the ground cinnamon and lemon juice.
Assemble. Arrange the apples on top of the base layer so that the base layer is fully covered with apples. Then drizzle caramel sauce over the apples so that each apple slice has caramel sauce on it. Sprinkle the topping over the apples so that the apples are evenly covered with the crumble topping.
Bake. Bake the apple tart for 30-35 minutes until set and browned on top.If the streusel starts browning too quickly before the apples are tender, you can loosely tent the tart with foil and continue baking until the apples are soft
Set. Allow the tart to fully set in the pan before slicing and serving.