Preheat oven to 180 degrees (circulating air). Grease a fireproof form or glasses with some coconut oil. Wash the plums, stone them and cut them roughly as required. Put the plum pieces into the glasses or baking tin.
Mix all dry ingredients with coconut oil to crumble and spread over the plum pieces. Bake the crumble in the oven for about 25 minutes until the crumbles turn light brown.