Peel and core the avocados and cut into thin slices. Drizzle with the juice of the lime. Make a dressing from the white wine vinegar, a little salt and pepper, a pinch of oregano and the walnut oil. Pour half of the dressing over the avocados, cover with foil and place in the refrigerator for 30 minutes.
Clean the mushrooms, cut into slices and drizzle with 2 tablespoons of lime juice. Wash the cherry tomatoes and cut in half. Peel and chop the shallot. Drizzle the remaining dressing over the mushrooms, tomatoes and cubed shallots and mix well. Arrange the salad on plates and spread the avocado slices on top.