01 - Heat vegetable oil in a large skillet or wok over medium-high heat. Add ground beef and cook, breaking apart with a spatula, until browned and cooked through, approximately 4–5 minutes.
02 - Add garlic, onion, carrot, and red bell pepper to the skillet. Stir-fry for 2–3 minutes until vegetables reach tender-crisp consistency.
03 - Add chopped cashews and sliced spring onions to the mixture, stirring constantly to distribute evenly.
04 - In a small bowl, whisk together soy sauce, hoisin sauce, oyster sauce, sesame oil, grated ginger, brown sugar, and chili flakes. Pour sauce over beef mixture and stir thoroughly to coat. Continue cooking for 1–2 minutes until heated through and fragrant.
05 - Remove from heat. Taste mixture and adjust seasoning as needed with additional salt, chili flakes, or a splash of lime juice.
06 - Spoon beef-cashew filling into individual lettuce leaves. Garnish generously with fresh cilantro leaves and accompany with lime wedges on the side.