Grease a casserole dish. Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Wash the pumpkin, cut in half, remove seeds. Cut into short sticks with skin. Clean, wash and slice the zucchini.
Clean the leek, wash thoroughly and cut into rings. Spread the vegetables in the casserole dish.
Coarsely grate the cheese. Whisk eggs, milk and cheese. Season with salt, pepper and nutmeg. Pour egg milk over the vegetables.
Bake the casserole in a hot oven for 45-60 minutes. If necessary, cover with aluminium foil about 15 minutes before the end of the baking time. Remove and arrange. Serve with salad.