In a medium-sized bowl whip vegan margarine and powdered sugar until fluffy and smooth.
Next, add flax egg, vanilla, and whisk until it becomes light and airy.
In the large bowl, combine rice flour, buckwheat flour, almond flour, baking soda, and baking powder.
Slowly add dry ingredients into the margarine mixture along with oat milk and lemon juice. Do not rush this process. Just add dry ingredients by a spoon and when it gets dry add a few tablespoons of milk and repeat.
When everything is combined you should have a smooth, creamy, and fluffy batter.
Pour the batter into a baking pan and top with chopped strawberries. Bake at 200°C (400F) for about 30 minutes.
Serve with powdered sugar and enjoy!