Add the remaining 3 tablespoons of oil to the skillet. Add the shallots and ginger and stir-fry over high heat until fragrant, about 1 minute. Stir the stock mixture, add it to the skillet and bring to a boil. Stir in the watercress, then stir in the shrimp and lime juice and season with pepper. Transfer the stir-fry to bowls, sprinkle with the peanuts and serve with rice.