Put ginger and chile oil into a medium bowl, mix until well combined, and set aside to marinate for 10 minutes.
Heat peanut oil in a wok or medium nonstick skillet over medium-high heat. Add ginger–oil mixture and stir-fry until ginger is crisp and deep mahogany brown in color, about 5 minutes. Strain ginger through a sieve, discarding oil, and set aside.
Bring a large pot of water to a boil over high heat. Add spinach and blanch until tender, 1–2 minutes. Drain, then plunge spinach into a large bowl of ice water to prevent it from cooking further. Drain again and gently squeeze out excess water. Put spinach on a wide shallow platter and cover with the reserved fried ginger.
Put soy sauce, vinegar, sugar and 1⁄4 cup cold water into medium bowl and stir until sugar dissolves. Spoon soy sauce mixture over ginger and around spinach on platter. Transfer to refrigerator to marinate for 20 minutes. Serve immediately.