Preheat your oven to 350°F. Line a cake pan or baking dish with parchment paper. This is optional, but it will ensure the cake comes out easily and minimizes sticking. I usually just serve this cake from the baking dish, so I skip this step.
Make the flax egg by combining 1 1/2 Tbsp ground flaxseed with 3 Tbsp warm water and setting it aside for 5 minutes.
In a large bowl, combine your plant milk, sugar or maple syrup, and vanilla extract. Add the flax egg once set and mix until everything is combined.
Add the dry ingredients to the bowl with the wet ingredients and stir until no clumps of flour remain. Be sure not to overmix in this step or the cake will come out dense and chewy.
Pour the cake batter into a cake pan or baking dish. Place the fruit directly on top of the batter.
In a medium-sized bowl, make the streusel topping by combining the rolled oats, whole wheat flour, granulated sugar, and avocado oil. Mix until you have a crumbly texture.
Once finished, sprinkle the streusel topping over the fruit.
Bake at 350 degrees Fahrenheit for 40-45 minutes or until a toothpick inserted into the center of the cake comes out clean.
Let the cake cool slightly, then slice and enjoy!