Mix the potatoes, carrots, kohlrabi and onions in a bowl. Add the bacon and salt, mix everything together. Using a tablespoon, create 9 mounds of the mixture on a baking tray lined with baking paper, flatten slightly.
Bake for approx. 20 mins. in the centre of an oven preheated to 200°C. Remove the rösti from the oven. Cut the cheese into strips and place on top of the rösti. Bake for about another 5 mins.