Mushroom Salad

This is a recipe from one of the few cookbooks I have: "Ketab'e Mostatabe Ashpazi" by Najaf Darya Bandari. It is in Farsi, my native language, and I completely enjoy reading his book which is by far more than just cooking instructions.
The recipe is for 3-4 servings, so I usually adjust it for one. Here is the recipe:

• 200 grams chopped mushrooms
• Chopped lettuce and spinach (filling an 8 oz measuring cup)
• 3-4 tomatoes 1 small onion (chopped like in onion rings)
• Vinegar Olive oil
• Salt and pepper

Combine all the ingredients to a container, and add the vinegar and olive oil with salt and pepper. Mix the ingredients throughly.

P.S. I used 'apple cider vinegar', also instead of onions I used green onions.