In a resealable plastic bag, stir together soy sauce, vinegar, sherry, five-spice powder, garlic, and ginger. Reserve 1/4 cup teriyaki mixture for salad. Add pork tenderloins to bag. Toss to coat. Marinate, refrigerated for 1 to 3 hours.
Preheat oven to 350 degrees F.
Heat 2 tablespoons oil in a heavy skillet over moderately high heat, Remove tenderloins from the bag, reserving marinade. Pat dry and sear on all sides in skillet, about 4 minutes total. Place skillet in middle of oven to finish cooking, about 20 minutes, or until an instant-read thermometer inserted diagonally in center of each tenderloin registers 140 degrees F. Let pork stand at room temperature 10 minutes. Slice into 1/2-inch slices.
In the same skillet, heat remaining tablespoon oil over moderately high heat and saute mushrooms, stirring occasionally, for 4 minutes. Add scallions and bean sprouts and cook 1 minute. Add reserved teriyaki mixture. Cook for an additional 2 minutes. Remove skillet from heat and add pork slices.
In a large bowl toss together spinach, cabbage, snow peas, and cucumber. Divide salad among 4 plates. Top with 1/4 pork mixture. Garnish with toasted peanuts and chopped cilantro.
Yield: 4 servings