Soak the kidneys in water, to cover, plus the vinegar for 1 hour. Drain and pat dry. Dredge kidneys in flour. Heat a large saute pan over high heat, then add the kidneys, and allow them to exude any excess water from their bath. Once the water has been exuded and evaporated, add the olive oil, garlic, mushrooms and potatoes and saute over high heat for 5 to 7 minutes, until the vegetables are soft and the kidneys are cooked through. Add the parsley and lemon zest, season with salt and pepper, to taste, and serve immediately.