Preheat oven to 180c / 350f.
Place plain flour, sugar and rolled oats into a bowl and mix lightly to combine.
Add melted butter and vanilla, mixing well to combine - the mixture should look "crumbly". Then set this crumble mixture aside.
Cut the green tops off the strawberries. Leave smaller ones whole, cut any large ones in half.
Place strawberries into a baking dish and sprinkle over sugar, then sprinkle over Cointreau liqueur and give everything a little mix around.
Using your fingers, place clumps of the crumble topping mixture over the top of the strawberries then bake for 30-35 mins, or until the crumble topping has browned and juice is bubbling up around the edges of the crumble.
Serve hot, topped with ice cream if you like.