Mix the fruit with lemon juice, corn starch and sugar, place in a tray.
In a large bowl, mix flour, sugar and cubed butter together. Use your hands to crumble the butter and make it sand-like, this is the crumble.
Put the crumble on top of the fruit, press it harder. Then sprinkle with brown sugar and some oat (Optional)
Pop in preheated oven at 190C, bake for 35-40 minutes or until is golden. Enjoy!