Preheat the oven to 375°F and line an 8"x8" baking pan with parchment paper.

In a medium sized bowl, stir together the oats, flour, brown sugar, and salt. Add in the melted butter (I used Earth Balance Vegan sticks)and vanilla; stir until combined.

Reserve about 1/3 of the oat mixture for the topping. Spoon in the remaining 2/3 of the crumble mix into your prepared baking pan and press to form a crust.

Bake for 10-13 minutes, or until the edges of the crust begin to lightly brown. Meanwhile, prep the filling.

For the filling:

In a small bowl, stir together the blueberries, raspberries, and strawberries (hull and cut the strawberries in small pieces) with the sugar, lemon zest and cornstarch. Spoon the berry filling over the warm crust and spread evenly with a spatula.

For the crumble:

Sprinkle the rest of the crumble mixture over the berry filling and try to cover as much of the berries as you can. There will be spots that aren’t completely covered.

Bake for 30-35 minutes, or until the crust and the crumble are golden and strawberries bubble just a little (mine was ready at just about 32 minutes. Every oven is different).

Cool completely before trying to remove from the pan. Let chill for a few hours in the refrigerator before slicing or you could dive right in as we did. If you choose to not wait, it will be very tricky to slice them and they will not stay intact.