Place rack in the center of the oven and preheat to 375°. Coat a 9" x 13" baking dish with cooking spray then set aside.
In a medium-sized mixing bowl, toss the diced apples with lemon juice to prevent browning then set aside.
Place oats in a food processor or blender then pulse until mixture becomes the consistency of coarse cornmeal.
Sift flour, baking soda and cinnamon into a small bowl then add the oat flour. Stir to combine then set aside.
In a large mixing bowl or the bowl of a stand mixer, cream butter and sugar together for approximately 4 minutes, until light and fluffy. Scrape down the sides of the bowl then add vanilla and salt. Begin beating and add the eggs one at a time, combining the first egg completely before adding the next.
Add half of the dry ingredients, stir to combine then add apple juice. Mix completely before stirring in remaining dry ingredients. Once batter is completely combined, fold in diced apples and 1/2 cup of chopped pecans.
When the apples and pecans are thoroughly mixed into the batter, transfer mixture to baking dish. Top with the remaining 1/4 cup of pecans, bake 25–30 minutes then remove from the oven and let cool completely.
While the cake cools, stir together the powdered sugar and milk for the glaze. Drizzle over the top of cooled cake, slice and serve.