Preheat the oven in 350ºF (180ºC).
Butter a 9-inch glass or ceramic dish.
In a small bowl mix sugar and cinnamon.
For the crumble, in a large bowl (or the bowl of a food processor) add flours, cocoa, brown sugar and lightly mix.
Add butter in pieces and work it with your hands or a dough cutter (or pulse if using the processor) until clumps begin to form.
Transfer to a medium bowl, mix in chopped chocolate or chips and reserve.
Peel, core and cut apples in half. Cut in half again so you have 4 quarters for each apple. Cut each piece in slices.
Add to the prepared dish and sprinkle with sugar/cinnamon mixture.
Drizzle with the lemon juice.
Top with the chocolate crumble mixture distributing evenly. It will look like it's too much but it's fine.
Bake for 35 to 45 minutes or until dry, bubbly and the apples are easily pierced.
Serve warm with ice cream or whipped cream.