Makes 4 main-course servings
• 2 bunches watercress (6 to 7 ounces each), thick stems trimmed, tender stems and leaves separated into bite-size sprigs, washed and dried
• 1/4 pound baby spinach, washed and dried
• 4 green onions (white and light-green parts), minced
• 1 tablespoon rice vinegar
• 2 teaspoons hoisin sauce
• 2 teaspoons soy sauce
• 1 teaspoon finely grated fresh ginger
• 2 tablespoons dark sesame oil
• 2 tablespoons vegetable oil, plus more for cooking the steak
• Kosher salt and freshly ground black pepper
• 11/2 pounds beef strip steaks (about 1 inch thick)
• 1 8-ounce can sliced water chestnuts, drained
Put the watercress and spinach in a large bowl, cover with a damp paper towel and refrigerate.
In a small bowl, whisk together the green onions, vinegar, hoisin, soy sauce and ginger. Whisk in the sesame oil and vegetable oil. Season to taste with salt and pepper.
Heat a large, heavy pan (preferably cast iron) over medium-high heat for at least 1 minute. Use paper towels to pat the steaks dry. Season them generously with salt and pepper, rub with oil, put them in the pan and cook until well-browned, about 4 minutes. Flip and continue to cook, about another 3 minutes for medium rare. Transfer the steaks to a cutting board, let rest for 5 minutes, and then slice them thinly.
Add the water chestnuts to the bowl of greens. Whisk the vinaigrette and toss the greens and water chestnuts with just enough of it to coat (a few tablespoons of vinaigrette should be left over). Taste and add salt and pepper as needed. Divide among four plates. Arrange the beef over the greens, drizzle with remaining dressing and serve.