Place a medium saucepan over medium heat. Add the olive oil and rice, and cook until the rice smells toasty, about 3 minutes. Add the chicken stock and half of the orange zest and juice. Bring to a boil, stir once more, then cover and reduce the heat to low. Simmer until tender and the liquid has been absorbed, 18 to 20 minutes. Remove from the heat and let stand, still covered, for 5 minutes. Stir the remaining orange zest and juice into the rice, and garnish with the green onions.