Preheat oven to 350°F and grease the bottom and sides of an 8x8 pan.
In a large bowl, combine all crust ingredients and mix with hands or a fork until just combined.
Press crust mixture into the bottom of the prepared pan and bake in preheated oven for 10 minutes. Remove from oven and cool on wire rack (don't turn off oven!!!)
In a skillet, heat 1 tbsp butter over low heat and add diced apples, tossing to coat evenly. Cook down for 5-10 minutes, until apples are soft. Remove from heat and stir in ¼ cup dulce de leche.
Pour mixture over baked crust.
In another bowl, combine ½ cup flour, ½ cup oats, ⅓ cup coconut sugar, and ¼ cup cold butter with a fork or hands until just combined.
Spread crumb topping over apple filling in pan. Bake for another 10-15 minutes, until crumb is golden brown.
Remove from oven and cool on wire rack. Drizzle with warmed dulce de leche before serving.
Recipe by Whisk & Shout at https://whiskandshout.com/apple-pie-streusel-bars-dulce-de-leche/