Preheat your oven to 350°F. In a bowl, combine the chopped apple, cinnamon, lemon juice, and 1 tablespoon of vanilla protein powder. Stir until the apples are well coated with the mixture. Transfer the coated apples to a small ramekin, spreading them evenly.
In a separate bowl or mug, mix together the oats, nut butter, remaining 1 tablespoon of vanilla protein powder, milk or water, and a pinch of salt. Use a fork or spoon to combine the ingredients until a crumbly mixture forms. If the mixture feels too dry to stick together at all, add a drop more milk or water to help it bind. I like to use almond butter for a richer flavor, but peanut butter works well too.
Sprinkle the prepared oat crumble from Step 2 evenly over the apples in the ramekin. Place the ramekin in the preheated oven and bake for 20 minutes, until the top is golden and the apples are bubbling underneath.
Remove the ramekin from the oven and let it cool slightly before serving. For an extra treat, top with your favorite ice cream, whipped cream, or an extra drizzle of nut butter. Enjoy your oven-fresh protein apple crumble!