Wash, peel and halve the kohlrabi, then cut into 2cm thick slices. Bring the vegetable stock to the boil in a pan and cook the kohlrabi over a low heat for about 15 minutes.
Cook the pasta in boiling salted water according to the pack instructions.
Meanwhile, wash the courgettes and cut into 1 cm dice. Peel and finely dice the onions.
Heat the oil in a pan and cook the onions until translucent over a medium heat. Add the flour and cook, stirring for 1 minute.
Drain the kohlrabi and reserve the stock in a bowl.
Slowly add the stock and milk to the onion pan and stir with a whisk. Bring to the boil, reduce the heat and simmer for about 10 minutes over a low heat, stirring occasionally.
Wash the parsley, shake dry and finely chop half the leaves.
Add the peas and courgettes to the sauce and bring to the boil. Fold in the chopped parsley and season with nutmeg, salt and pepper.
Drain the pasta and place them in a baking dish.
Spread the kohlrabi, the pea sauce, emmental cheese and sunflower seeds on top. Bake in a preheated oven at 200°C (180°C fan, gas 6) for 25 minutes. Garnish with parsley leaves and serve.