1. Stir together fish sauce (or soy sauce) and brown sugar in a small bowl. Arrange lettuce on a platter or individual plates.
2. Heat 2 tsp. oil in a large nonstick skillet over high heat until hot but not smoking. Stir-fry beef, in batches, until browned on the outside and still pink inside, 30 seconds to 1 minute per batch. Spoon over lettuce.
3. Add the remaining 1 tsp. oil to the skillet and cook chili peppers, onions and garlic, stirring occasionally, until softened, about 1 minute. Add the fish-sauce (or soy-sauce) mixture and bring to a boil, stirring. Remove from the heat and stir in orange and cilantro. Spoon over lettuce and beef, sprinkle peanuts over top and serve warm.

Yield: 4 servings