1. Place beef on a plate and let the beef rest at room temperature for 30 minutes. Rub salt and pepper onto all sides of the beef, cover with plastic wrap, and leave for another 15 minutes.
2. Heat two tablespoons of vegetable oil in a frying pan over medium-high heat and brown all sides of beef, about 1 - 3 minutes. Place the beef on aluminium foil and wrap it tightly. Let rest for 30 minutes.
3. Heat 1 teaspoon of vegetable oil in a frying pan over medium heat. Add celery, onion, garlic and shoyu. Lightly stir-fry the vegetables and bring to a boil. Once boiled add vinegar and turn down the heat.
4. Slice the beef into ½ inch slices. Plate and use the watercress as a side. Drizzle the sauce over the salad and beef.

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