Blend the oats and the almonds in a blender or food processor until finely ground. Roughly crush the walnuts with a knife.
Wash and peel the carrots. Grate them using a grater or the grating blade of your food processor.
Combine the oat flour, almond flour and grated carrots in your food processor by pulsing several times. Alternatively, add everything to a large mixing bowl and combine with a spatula.
Add the date syrup, spices and vanilla extract to a mixing bowl. Combine with a spoon.
Pour the date syrup into the food processor and pulse until combined. The mixture should be sticky and hold its shape when you press it between two fingers.
Line an 8" square pan (20 cm) with parchment paper. Transfer the mixture into the pan and press down firmly with a spoon or spatula. If you want, you can smooth the surface with wet fingers. Place in the fridge to set while you make the frosting.