Heat a wok or large skillet over medium-high heat until hot enough to sizzle a drop of water. Add oil, celery and the orange zest. Stir-fry until the celery is crisp-tender, but still bright green, 3 to 4 minutes. Stir in ginger and garlic. Add the orange juice mixture and onion and stir-fry just until the sauce thickens, about 1 minute. Serve sprinkled with peanuts.