Preheat the oven to 350°F (175°C) and grease a 8x8-inch baking pan or line it with parchment paper for easy removal.

In a saucepan over medium heat, combine the diced apples, water, honey, lemon zest, ground cinnamon, and ground nutmeg. Cook the mixture, stirring occasionally, until the apples become tender and most of the liquid has evaporated, about 5-7 minutes. Remove from heat and stir in the vanilla extract. Set aside to cool.

In a large mixing bowl, combine the rolled oats, ground flaxseed, almond flour, baking powder, and salt.

In a separate bowl, combine the apple sauce, nut butter, and vanilla extract.

Pour the wet ingredients into the dry ingredients and mix thoroughly. Add the chopped nuts to the mixture and stir until evenly distributed.

Spread 2/3 of the flaxseed mixture into the prepared baking pan, pressing it down evenly to create a firm base.

Spread the cooled apple filling evenly over the flaxseed base. Crumble the remaining 1/3 of the flaxseed mixture over the apple filling, creating a crumbly topping.

Place the baking pan in the preheated oven and bake for 25-30 minutes, or until the top is golden brown and the filling is bubbling.

Allow the squares to cool in the pan for about 10-15 minutes. Then, using a sharp knife, cut them into squares or rectangles. Let them cool completely before removing them from the pan.

While the squares are cooling, prepare the topping by whisking together the Greek yogurt, peanut butter, and cinnamon until well combined and a mousse is formed. Add mixture to a piping bag or ziploc bag with the corner tip cut off. Gentle squeeze the yogurt peanut butter mousse to each square. Serve and enjoy!