Boil potatoes in water til tender. Drain and mash potatoes. In a separate pan, saute onions and mushrooms in oil and water over medium-high heat for three minutes. In a large bowl, mix mashed potatoes, sauteed onions and mushrooms, seasonings and matzo meal together in a large bowl. Form 10 croquettes. Heat oil in a large frying pan over med-high heat and fry croquettes for 8 minutes on each side. Serving size is 2 croquettes per person.