Combine 250g flour, 3 eggs, water, and 1 pinch freshly grated nutmeg in a bowl. Mix well, then cover and let rest for 30 min.
Coarsely grate the Hokkaido pumpkin with its skin.
Dice the onions and sauté in clarified butter over medium heat. Transfer half to a plate and set aside.
Add the grated pumpkin to the remaining onions in the pan and fry for 5 min over medium heat. Season well with salt and pepper. Remove from heat.
Preheat oven to 180 °C (350 °F) with fan-assist.
Coarsely grate the cheese.
Bring a pot of salted water to a boil. Cook the spaetzle until just tender. Drain well.
In a bowl, mix the cooked spaetzle with the pumpkin mixture. Spread half into a baking dish and sprinkle with half the cheese. Top with remaining spaetzle mixture and sprinkle with remaining cheese.
Bake for 10 min until the top is golden.
While baking, reheat the reserved onions in a pan over medium heat with the remaining clarified butter until crispy.
Remove from oven, top with fried onions, and serve with lettuce.