Prep & Soak:

Preheat oven to 350°F. Grease a 9x5-inch loaf pan thoroughly with cooking spray, getting all corners and sides.

In a medium bowl, combine 1/2 cup oats with 1/2 cup milk. Stir well and let sit for 20 minutes to soften the oats.

Mix Wet Ingredients:

In a large mixing bowl, whisk together applesauce, eggs, maple syrup, brown sugar, oil, and vanilla until smooth with no egg streaks.

After the oats have soaked for 20 minutes, add them to the wet mixture and whisk until fully combined.

Combine Dry Ingredients:

In a medium bowl, mix together flour, apple pie spice, baking powder, baking soda, and salt. Whisk for about 30 seconds to distribute the leaveners evenly.

Bring It Together:

Pour the dry mixture into the bowl with wet ingredients. Using a rubber spatula or wooden spoon, gently fold together until just combined and no dry flour remains. Don't overmix - the batter should look thick and slightly lumpy.

Scrape batter into the prepared loaf pan and spread evenly corner to corner. Tap the pan on the counter 2-3 times to release air bubbles.

Make Streusel:

In a small bowl, combine remaining oats, brown sugar, and cold butter pieces. Use your fingers to rub and pinch until the mixture is crumbly with butter distributed throughout.

Scatter streusel topping evenly over the batter. Don't press down.

Bake:

Bake on the center rack for 50-60 minutes, until a toothpick inserted in the center comes out clean or with just a few moist crumbs. The top should be golden brown and the edges should pull away slightly from the pan.

If the top browns too quickly, tent loosely with aluminum foil for the last 15 minutes.

Cool & Serve:

Remove from oven and let cool in the pan for 15 minutes. Run a butter knife around the edges to loosen, then flip out onto a wire rack.

Let cool completely before slicing (about 1 hour) for the best texture and clean slices.