In a mixing bowl, add all dry ingredients (flour, baking powder, cornstarch, baking soda, cane sugar and salt). Mix together until well combined.
In a different bowl whisk together olive oil, milk and mango juice.
Add wet ingredients to dry ingredients while mixing with an electric stand or hand mixer. Go slowly from low to high speed while mixing. Mix until well combined, but don’t over mix! You’ll end up with a rather “thin” batter, it shouldn’t be too thin though! Set aside.
Add all dry ingredients (quick oats, sugar, flour) for the streusel into one bowl and mix roughly.
Then slowly pour oil (or melted butter) into the dry ingredients and with a fork. Mix until you got a nice crumble.
Pour batter into prepared baking sheet and smooth down if necessary.
Scatter peach pieces all over the batter. Try to work quick, so the pieces won’t sink into the batter too much. Then crumble the streusel on top of everything.
Bake in preheated oven for around 30 minutes. (Bake a bit longer if necessary)
Take cake out of the oven and let it cool down entirely in the baking sheet before cutting it into pieces. It is a very moist and tender cake, so cutting it when still warm may lead to pieces that fall apart. Enjoy with freshly brewed coffee or !