Preheat the oven to 190C (375F). Grease a large square or rectangular baking dish (I used a 28cm square, 7 cm deep dish) and set aside.
Deseed and cut all the plums into quarters. Place the plums into the baking dish.
Put the white sugar, flour, and ground cinnamon, ground ginger into a bowl and mix it with a fork. Sprinkle the sugar mixture over the plums and coat all the plums evenly. Sprinkle zest over the plums, then pour the lemon juice over the plums and mix well.
Place some baking paper or tin foil over the baking dish and poke some holes into it so that the steam can escape. Bake for 25 minutes for firm and 30 minutes for soft baked plums.
Prepare the topping before the plum base comes out of the oven. Place all the topping ingredients into a big bowl. Mix with a fork until well combined and small chunks of dough are formed. Sprinkle the crumble over the baked plums. Bake for around 15 minutes or until golden.
Serve warm with some vanilla ice-cream. Store covered in the fridge for up to 5 days. Heat in the microwave or oven before serving again.
Servings 0
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.