Arrange the olive oil to heat in a saucepan. Sauté the onion and garlic. Add the mushrooms. Add the tomato, sobrasada and marjoram. Season with salt and pepper. Cook for five minutes with moderate heat. Sauté the rice for about three minutes. Pour half a liter of boiling vegetable broth. Add more broth several times during cooking as the rice absorbs the liquid. Add the spinach in three minutes to finish cooking the rice. Add the grated cheese. Remove the casserole from the heat. Let the rice rest for a few minutes before serving.