Halve the chicken fillets, wash and pat dry. Fry in hot fat while turning for about 15 minutes. Season with salt and pepper. Cook the noodles in boiling salted water for about 10 minutes.
Peel and finely dice the onion and garlic. Fry in hot oil. Add spinach without defrosting and let thaw at low heat. Season with salt and pepper. Drain the pasta. Remove the chicken fillets from the pan.
Sweat the flour in the frying fat. Add milk bit by bit and stir until smooth. Add lemon juice and zest and let it swell at low heat for about 10 minutes. Grate cheese and stir into the sauce.
Season the sauce with salt, pepper and nutmeg. Cut the chicken meat into slices. Put the noodles, spinach and chicken in a flat casserole dish. Pour sauce over it. Bake in a preheated oven (electric cooker: 200 °C/ gas: level 3) for approx. 35 minutes.
Possibly garnish with lemon slices and parsley.