Preheat the oven to 350F and butter a 9"x9" glass baking dish.
In a large bowl, whisk together flour, salt, baking powder, baking soda and cinnamon. Add butter and honey and cut with a pastry cutter, two knives or your hands until the mixture is moist and crumbly, about the size of peas. (Do not cheat and use a stand mixer to do this for you otherwise the bars will not turn out.)
Add oats and again, use a pastry cutter, two knives or your hands to evenly distribute the oats Be sure to not allow the butter to melt.
Measure 2 cups of this mixture and press down into the bottom of the prepared glass pan.
Peel one apple and set peel aside. Dice the apple into ¼" pieces. Measure 2 cups worth into a medium bowl. Repeat with the second apple if additional apple is needed to reach 2 cups. (I used 1¼ large apple to reach 2 cups.)
Place the peels and any remaining apple along with vanilla and lemon juice into a blender and puree until mostly smooth. It is okay if some pieces are large, but no larger than ¼". Add this mixture to the diced apples and stir to combine well.
Pour apples evenly over the dough. Using a spatula, evenly distribute and press down the apple mixture.
Crumble the remaining dough evenly over the top and again, press down lightly.
Bake until the top is golden brown, approximately 25-30 minutes. Allow the bars to cool completely before cutting. Cutting the bars before they have completely cooled will cause the bars to crumble.
When cutting, gently use a "sawing" motion, rather than a slice and drag, in order to get a better "bar."
Store in the refrigerator. Bars will be even more "bar" once chilled.