Prep the pan and oven: Heat oven to 325°F (160°C). Line a 9-inch springform pan with parchment on the base and lightly grease the sides.
Make the crust: In a bowl, mix 1 cup rolled oats, 1/2 cup almond flour, 2 tablespoons granulated sweetener, 1/2 teaspoon cinnamon, a pinch of salt, and 3 tablespoons melted butter or coconut oil.
Press firmly into the pan. Bake for 8–10 minutes until lightly golden. Cool slightly.
Cook the apples: Peel (optional) and dice 2 apples.
In a skillet over medium heat, add apples, 1–2 tablespoons maple syrup, 1 teaspoon lemon juice, 1/2–1 teaspoon cinnamon, a pinch of nutmeg, and 1–2 tablespoons water. Cook 4–6 minutes until just tender. Stir in 1 teaspoon cornstarch mixed with 2 teaspoons water and cook 30 seconds to thicken.
Remove from heat and cool.
Mix the filling: Beat 12 ounces reduced-fat cream cheese until smooth. Add 1 cup plain Greek yogurt, 1/2 cup granulated sweetener, 2 teaspoons vanilla, and a pinch of salt; mix until creamy. Beat in 2 eggs, one at a time, just until combined.
Fold in 1/2 cup vanilla protein powder gently to avoid overmixing.
Assemble layers: Pour the filling over the par-baked crust. Spoon the cooled apples evenly over the top and gently swirl a few times with a knife to nestle them without fully mixing.
Make the crumble: Mix 3/4 cup rolled oats, 1/3 cup almond flour, 3 tablespoons brown sugar, 1/2 teaspoon cinnamon, a pinch of salt, and 3 tablespoons melted butter. Sprinkle evenly over the apples.
Bake low and slow: Bake at 325°F (160°C) for 40–50 minutes.
The edges should be set and the center slightly wobbly like Jell-O. If the crumble browns too quickly, tent loosely with foil.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake sit for 20–30 minutes. Then transfer to a rack and cool to room temperature.
Chill to set: Cover and refrigerate at least 6 hours, preferably overnight.
This step is essential for clean slices and the right texture.
Serve: Run a knife around the edge before releasing the springform. Slice with a warm, clean knife. Optional: finish with a light drizzle of maple syrup or a dollop of yogurt.