Lunchtime Rooty Bircher

100g celeriac

1 medium apple

100g jumbo oats

50g raisins or sultanas

50g whole, skin-on almonds

50g mixed seeds, such as sunflower, pumpkin and sesame (or just one type if you prefer)

3 tbsp extra virgin olive or rapeseed oil

Juice of ½ lemon

200ml cloudy apple juice

Sea salt

black pepper