In a wok (or large non-stick fry pan) over high heat, heat 2 tablespoons of peanut oil until oil begins to smoke. Add chicken and stir fry until browned on all sides.Remove and let drain. Meanwhile, add remaining 2 tablespoons of peanut oil and sesame oil into wok and return to high heat. Quickly cook together ginger and garlic for 10 seconds or until fragrant. Add rice, pistachios, peas and scallions and continue stir frying for 2 minutes, stirring often. Add chicken, oyster sauce, water, mustard and soy sauce and let cook 3-5 minutes or until hot throughout. Remove from heat and season with salt if needed.Lightly toss mustard greens in sesame oil.
Mold warm fried rice onto warm serving plates and garnish with greens, pistachios and bean sprouts.