This easy beef stir-fry will save you from take-out Chinese every time.
Season 1 1/4 pounds beef sirloin, cut into 2-inch-long slices about 1/4 inch thick, with 1/4 teaspoon each salt and pepper. In a large skillet, heat 1 tablespoon canola oil over medium-high heat. Add beef to skillet; cook, tossing occasionally, until brown, 2 to 3 minutes. Transfer to a plate with a slotted spoon.
Reduce heat to medium. Add 1 tablespoon minced fresh ginger and 3 stalks celery, sliced 1/2 inch thick diagonally; cook until celery is soft, about 4 minutes.
Add 2 bunches watercress, trimmed and washed; toss until wilted, about 1 minute. Return beef with any juices to skillet; stir in 1 tablespoon toasted sesame oil, 1 tablespoon rice vinegar, and 1 tablespoon soy sauce. Serve hot over rice.