Preheat the oven to 375F. Lightly grease a 12" cast-iron skillet with vegan butter.
Start by making the crisp topping: In a medium mixing bowl, combine the flour, oats, sugar, baking powder, cinnamon and salt. Add the vegan butter and combine it with the dry ingredients using your finger until everything is moist and clumps together. Set it aside in the fridge while you prepare the rest of the recipe.
In a medium-large mixing bowl, whisk together the lemon juice, brown sugar, 2 tablespoons of flour, vanilla, cinnamon, salt and water.
Peel and dice your apples into small cubes. You can also do slices if you prefer. Place it in the lemon/brown sugar/flour mixture. Toss until evenly coated.
Spread the apples in the prepared cast-iron skillet. Top with the crisp topping.
Bake for 40 minutes at 375F until the topping is golden. Remove from the oven and serve warm or cold. It's also delicious served with (vegan) ice cream.