Preheat oven to 350°F.
Mix the flax meal and water together in a small bowl and set aside.
Mix together the oat flour, baking soda, salt and cinnamon.
Blend the dates, almond milk and vanilla in the blender until smooth.
Stir the blended mixture into the dry ingredients.
Fold in the flax egg, mashed bananas and pineapple.
Fold in 1 1/2 cups of the walnuts.
Divide mixture between 3 parchment lined cake pans (9 inch)
Bake for 35-40 minutes.
Let cool
Add all frosting ingredients except for the 2 Tbsp of water to blender and blend until smooth.
Add remaining water if necessary while blending frosting.
Place cake on a cake tray or plate.
Smooth on about 1/2 cup of the frosting onto the top of that cake.
Add second cake to the top of that.
Smooth on about 1/2 cup of frosting onto the top of that cake.
Add third cake and use remaining frosting to frost entire top and sides.
Sprinkle remaining walnuts on top of cake.
Keep in the refrigerator for up to a week.