Whisk hoisin sauce, soy sauce, sesame oil, and garlic together in a bowl. Set aside.
Bring about 4 cups water to a boil in a large deep skillet. Add green beans and boil for 3 minutes. Drain green beans and run under cold water for 1 minute.
Bring hoisin mixture to a simmer in the same skillet over medium-high heat. Add green beans.