Cook rice according to the packaging instructions. Set aside and let it cool down.
Wash mushrooms and cut in a slice in semi-thin slices. Heat up 1-2 tbsp of olive oil and add mushrooms and season with a pinch of salt and pepper. Cook for up to 10 min and set aside.
Chop peppers, cheese, and ham into medium size cubes.
In a large bowl mix together all ingredients following with mayonnaise and dried oregano. Season to taste with salt and pepper.
Let it chill in the fridge for at least 2 hours before serving.