Bring about 3 quarts of water to a boil. Add the beans, return to a boil, and simmer until crisp-tender, about 3 to 4 minutes. Drain and set aside.
Heat the olive oil over medium heat. Add the beans, garlic, sage, a pinch of the salt and several grinds of pepper. Cook, stirring occasionally, until the beans are browned in places, about 3 to 4 minutes. Stir in the pine nuts, lemon zest, and prosciutto. Season with lemon juice and zest, and add more salt and pepper to taste.