Cook the spaetzle in plenty of boiling salted water for 15-18 minutes. Drain. Cut the leek into 1/2 cm thick rings and blanch in boiling salted water for about 1 minute. Then drain on a sieve. Core the tomatoes as desired and cut into medium-sized cubes. Cut the onion into fine rings. Heat 1 tablespoon of oil. Fry the onion rings in it for about 10 minutes over medium heat until golden brown. Heat the rest of the oil, fry the spaetzle in it for 2-3 minutes, turning. Spread the cheese on the spaetzle, let it melt briefly and deglaze with the broth. Season to taste with salt and pepper. Fold in the leek rings. Add the tomato cubes. Sprinkle with the roasted onion rings.