Preheat the oven on 180 degrees Celsius or 354 degrees Fahrenheit.
Mix the flour, butter, 3 tablespoons of sugar, pinch of salt, pinch of cinnamon and oats. Make sure you use very cold butter. Everything needs to be mixed, however it needs to stay crumbly.
Cut the apple in pieces (1 by 1 cm) and clean the strawberries. Depending on the size of the strawberries, you could cut these in half as well.
Mix the apple, strawberries, zest of an orange, lemon juice and sugar.
Butter the oven dish. Add the fruits and top off the with the crumble. Bake for 25-35 minutes in the preheated oven. Serve with some icing sugar!