Trim the ends off the beetroot and cut into quarters. Trim the ends off the carrot and roughly chop. Peel and core the apple and cut it into quarters.
Place the beetroot, carrot, apple, olive oil, lemon juice and mint into the Thermomix bowl. Chop for 2 sec/speed 5. This might be enough, but if not, scrape down the sides of the mixing bowl with a spatula and stir the beetroot mix well. Chop again for 1 sec/speed 5. Avoid over-chopping; otherwise, it will turn into a dip! Season to taste, and add more lemon juice if desired.
Transfer the beetroot salad to a serving dish. Toss in the rocket and crumble over the feta cheese.
Serve immediately or refrigerate for later.
Notes
Storage: Store the salad in an airtight container in the fridge for up to 3 days.