1.Heat a grill plate (or barbecue or grill). Rub the steak with the oil, sprinkle with salt and pepper. Cook steak over high heat until browned on both sides and cooked as desired. Transfer to a plate, stand, covered, for 10 minutes; slice steak thinly.
2.To make nam jim dressing, blend or process all ingredients until smooth.
3.Arrange salad leaves, cucumber, shallots, steak and cashews on a platter. Drizzle with dressing and top with coriander leaves, if desired.