Peel and chop the onion. Clean, wash and cut the bell peppers into small pieces. Clean, wash, halve and slice the zucchini. Heat the oil in a medium ovenproof pan. Brown the onion, bell pepper and zucchini. Season with salt, pepper and oregano.
Mix eggs, milk and sour cream. Season with salt and pepper. Pour the egg milk over the vegetables and let it stand in the preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: level 3) for 30 minutes. Remove the tortilla, let it cool down and cut it into pieces. Arrange the tortilla on a plate and serve garnished with marjoram
Waiting time approx. 1 hour