Prepare. Prep you apples as indicated (peel and chop). Also, prepare your loaf pan for nonstick and preheat your oven to 350° F.
Apples. Place your chopped apples into a mixing bowl. In a small bowl, use a fork or a whisk to combine together the sugar, cinnamon, and nutmeg. Pour half of the mixture over the apples, toss the apples, and add the remaining mixture and toss until the apples all have mixture on them.
Batter. In a large mixing bowl, combine together the flour, baking powder, and sugar. Once combined, make a well in the center of the ingredients. In another bowl, combine together the oat milk, oil, and vanilla extract. Once fully combined, pour the mixture into the well that you created in the batter and mix until just combined.
Streusel To make the streusel crumble topping, in a small bowl combine together the light brown sugar, flour, and ground cinnamon. Once combined, add the water and neutral oil and mix (you can use your hands) until the mixture forms a crumble.
Assemble. For the bottom layer, evenly spread about a third of the batter into the bottom of your prepared loaf pan. On top of the batter, place about half of the apple mixture evenly spread out. Top the apples with another layer of the batter (half of what is left) evenly spread out. On top of the batter, add most of the remaining apples, leaving a few for the topping, and then top that layer with the remaining batter.
Topping. Evenly spread the remaining apples over the top layer of batter in the pan. Then evenly spread the streusel on top of the ingredients in the loaf pan.
Bake. Bake your apple crumble loaf until in is golden brown around the edges and a toothpick comes out clean from the center (about 50-60 minutes).
Cool Allow the loaf to cool in the pan for 20 minutes. You can carefully run a butter knife around the edges of the loaf to loosen it if needed before placing a cooling rack over the pan and inverting the loaf when removing it.