Heat oil in large skillet over medium heat. Add potatoes, ginger, garlic, cumin and turmeric; cook, stirring, 3 minutes. Add 2 cups water, cover and cook until potatoes are tender, about 10 minutes. Raise heat to high, uncover and cook until liquid is reduced to 1/4 cup, about 8 minutes. Stir in arugula to wilt; season.