Wash the potatoes, bring to the boil covered with water and cook for about 20 minutes. Drain potatoes, rinse, peel and slice. Peel and slice carrots and cook in boiling salted water for 5 minutes.
Clean, wash and slice the zucchini. Melt the fat in a saucepan. Sauté flour in it, deglaze with milk and bring to the boil while stirring. Add cheese and let it melt.
Season to taste with salt, pepper and nutmeg. Grease a casserole dish. Put turkey, potatoes, carrots and zucchini with the sauce in layers in the dish. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes.
Serve the vegetable casserole garnished with basil.