Put oat flakes, ground almonds, spelt flour and salt in a mixing bowl and mix together.
Drizzle the oil, the sweetener and vanilla over the dry ingredients and lightly mix.
Slice apples (or pears) into bite-sized pieces.
Add berries and put the fruit in a baking dish (big enough to accommodate all fruit and the crumble topping). Add the apple juice.
Cover with the crumble mixture and top with some sliced almonds.
Cover lightly with foil (do not tuck it under the rim) and place in a pre-heated oven (gas mark 6) for 45 mins, removing the foil after 25mins of baking to allow the top to become crisp and golden. Check from time to time and turn the heat down if necessary.