Pat the 800g cubed beef very dry with paper towels, trimming any uneven pieces so every cube sits close to 2.5–3cm and cooks at the same rate. In a bowl, combine the 4 minced garlic cloves, 1½ tbsp oyster sauce, 1 tbsp fish sauce, 1 tbsp light soy sauce, 1½ tsp sugar, ½ tsp black pepper and 1 tbsp neutral oil, stirring until the sugar has dissolved. Add the beef and toss until every cube is evenly coated and glossy, with no pool of liquid left in the bottom of the bowl. Cover and marinate for 30 minutes at room temperature if your kitchen is cool, or in the fridge if it needs to wait longer, but never for hours. That short, light marinade is what seasons the surface without making the beef so wet that it steams in the pan.

As soon as the beef is marinating, rinse the 200g jasmine rice in cold water 2–3 times, swirling it with your fingers, until the water runs mostly clear, then drain well. Combine the rice and 300ml water in a small saucepan and bring to a boil over medium-high heat. Stir once, cover tightly, reduce to the lowest heat and cook for 12 minutes, then turn off the heat and leave it to stand, still covered, for 10 minutes without lifting the lid. Fluff gently with a fork and keep it covered and warm. The grains should be soft, separate and fully ready before the beef goes anywhere near the wok. That timing matters because shaking beef is best eaten the moment it leaves the pan, while it is still glossy and juicy.

While the rice cooks, wash the lettuce and dry it thoroughly, tearing any large leaves into manageable pieces. Slice the 2 tomatoes and the ½–1 English cucumber, pick the 10–15g cilantro leaves and cut the 2 limes into wedges. Cut the small onion into thin wedges or separate it into petals, and slice the 3 scallions, setting about a third of the green tops aside for the garnish. Once the rice is fluffed, divide it among 4 bowls or plates and arrange the lettuce, tomato and cucumber beside it, keeping the vegetables cold and crisp. Set the cilantro and lime wedges within reach of the stove. That advance plating is what lets the beef go straight from the wok onto the rice without losing its heat or its gloss.

Heat a wok or large heavy skillet over high heat for 2–3 minutes, until very hot and just beginning to smoke. Add ½ tbsp of the neutral oil and swirl it around the pan. Add half the beef in a single layer and let it sear undisturbed for about 1 minute, until a deep brown crust forms underneath. Then toss or "shake" the pan frequently, cooking for 2–4 minutes in total depending on cube size and preferred doneness, until the outside is deeply browned, the edges look glossy and caramelised and the centres still feel tender when pressed. Transfer to a plate, let the pan reheat fully, then repeat with another ½ tbsp oil and the remaining beef. If the cubes release liquid and start to simmer, the pan is crowded or not hot enough. That fast, uncrowded sear is what browns the beef deeply without overcooking its centre.

Reduce the heat slightly to medium-high and add the remaining ½ tbsp neutral oil, which the pan usually needs after 2 batches. Add the onion and stir-fry for 30–60 seconds, just until it softens slightly at the edges but still holds its shape. Add the 2 tbsp unsalted butter and let it melt and foam. Return the beef with any juices from the plate, add the remaining two-thirds of the scallions and toss everything together for 30–60 seconds, just until the beef is coated, glossy and heated through. Taste and adjust with a tiny splash of extra fish sauce or a pinch of extra black pepper only if needed. The sauce should lightly glaze the beef rather than pool in the pan; if it looks watery, toss for a few seconds longer over high heat. That brief final toss is what melts the butter into the juices to form a glaze without cooking the beef any further.

Spoon the hot shaking beef, onion and every bit of glaze over or beside the rice in each prepared bowl, giving every serving about a quarter of the beef. Scatter over the reserved scallion greens and the cilantro leaves, then tuck the lime wedges alongside. Serve immediately, while the beef is still steaming and the vegetables are still cold and crisp. Squeeze the lime over the beef and vegetables at the table, or wrap bites of beef and tomato in the lettuce leaves. The finished bowl should show deeply browned cubes with a thin, shiny coating, never a pool of thick gravy. That contrast between the hot, rich beef and the cool, crisp vegetables is what makes the dish feel genuinely balanced rather than heavy.