Preheat your oven to 375°F (190°C).
Core and dice the apple into bite-sized pieces, leaving the skin on for extra fiber.
Place the diced apples in a small oven-safe ramekin or baking dish and toss with the water and half of the cinnamon.
In a small mixing bowl, combine the rolled oats, vanilla protein powder, sliced almonds, sea salt, and the remaining cinnamon.
Melt the coconut oil and drizzle it over the oat mixture, stirring until a crumbly texture forms.
Spread the crumble mixture evenly over the apples in the baking dish.
Bake for 20 to 25 minutes until the apples are tender and the topping is golden and fragrant.
While the crumble bakes, whisk the Greek yogurt and vanilla extract together in a small bowl until smooth.
Remove the crumble from the oven and let it cool for 5 minutes.
Serve the warm apple crumble with the vanilla Greek yogurt dolloped on top.