Clean the mushrooms and cut them into slices. Dice the tomatoes. Core the peppers and cut into bite-sized pieces. Cut the white lower part of the spring onions into thin slices and sauté them in a saucepan in the oil.
Add the mushrooms, tomatoes, peppers, rice and vegetable stock to the saucepan, bring to the boil and simmer over low heat for about 20 minutes, until most of the liquid has been absorbed by the rice and the vegetables are soft.
Just before the end of the cooking time, stir in the crumbled feta. Season to taste with pepper and salt. Cut the green part of the spring onions into fine rolls and pour them over the food on the plate. Serve sprinkled with the grated Pecorino Romano.