Line a 13 cm cake tin with parchment paper and preheat the oven to 180°C (360°F).
Blend the oats into flour, then mix with almond flour and ground cinnamon.
Grate the carrots and apple finely.
Soak the raisins in cold water for 15 minutes, then drain.
In a bowl, whisk yogurt or sour cream, eggs, salt and sweetener until smooth.
Add grated carrots, grated apple, orange zest, melted coconut oil and drained raisins, and mix well.
Activate the baking soda with lemon juice and stir it into the wet mixture.
Add the oat and almond flour mixture, fold until combined and let the batter rest for 10 minutes.
Pour the batter into the prepared tin and bake for about 40 minutes, until a toothpick comes out clean, then cool completely.
Mix cottage cheese or ricotta with yogurt until creamy, roast walnuts in a dry skillet for 2–3 minutes, then spread the cream over the cooled cake and decorate with roasted walnuts and grated carrot pieces.