Cook the tortellini in about 1/2 litre of salted water for about 9 minutes. Chop onion and garlic finely. Wash and chop the tomato. Wash and slice the mushrooms. Heat oil in a pot. Fry onion and garlic. Add the mushrooms and fry them for about 5 minutes, turning them until golden brown.
Add tomatoes and steam briefly. Season with salt and pepper. Deglaze with 3-4 tablespoons of water and strained tomatoes. Bring to the boil, add Oreagano and simmer for about 5 minutes. Season sauce with salt and pepper. Mix with drained tortellini and garnish