Combine the oats, almond flour, brown sugar and butter in a bowl. Use your hands to mix until well combined and a dough-like mixture forms.
Press ⅔ of the mixture into a parchment-lined 20 × 20 cm pan. Bake for 10 minutes, then set aside.
Add the apples, maple syrup, vanilla, cinnamon and cardamom to a saucepan. Cook over medium-high heat for 7–9 minutes, until the apples start to soften.
Mix the lemon juice and cornstarch until smooth. Remove the apples from the heat, stir in the mixture and continue stirring until the filling thickens.
Spread the apple filling evenly over the crust. Sprinkle the remaining crust mixture over the top.
Bake at 175°C for 25–30 minutes, until bubbling around the edges and golden brown on top.
Meanwhile, whisk the almond milk and powdered sugar until smooth.
Let the bars cool completely. Cut into 16 squares and drizzle with the icing.