Place half the lemon juice in a large bowl. Halve and core apples. Thinly slice. Add apple to lemon juice (see top tip). Gently toss to coat.
Combine mayonnaise and remaining lemon juice in a bowl. Season with salt and pepper. Thinly slice celery stalks. Chop leaves.
Add celery, celery leaves and beetroot to apple mixture. Gently toss to combine.
Top tip:
Tossing sliced apple in lemon juice prevents the apple turning brown.
*Although not traditionally counted; beetroot is providing the 1g protein per serve