Melt butter in a medium saucepan over medium heat; add mushrooms, cook until tender, about 3 minutes. Add peas and water; bring to the boil; add risoni, simmer, stirring occasionally for 10 minutes or until tender. Add cheese, stir until melted.
TIP: This is enough for 2 servings. When reheating the second serving, simply add a small amount of water to loosen the risoni and reheat, adding more water if necessary. Keep refrigerated for 1 day.
