Fill a 4 1/2- to 5-quart stockpot halfway with water. Bring to a boil over high heat. Fill a bowl with cold water and several cups of ice. Add green beans to boiling salted water. Cook 3 to 5 minutes or until al dente. Drain and shock beans immediately in the ice bath. When cool, drain and pat dry. Cover with plastic wrap, and chill 30 minutes or up to 1 day.
Combine butter and olive oil over medium-high heat in a sauté pan, and sauté shallot and 1 teaspoon zest until translucent and soft, about 1 to 1 1/2 minutes. Add beans, and season with kosher salt and pepper. Sauté until beans are warmed through, about 30 seconds. Transfer to warmed platter, garnish with remaining 1 teaspoon zest, and serve immediately.