Combine the chopped cilantro, 1 tablespoon sugar, and the next 4 ingredients (through soy sauce) in a large zip-top bag. Add beef; let stand 15 minutes. Remove the beef from the marinade. Reserve the marinade.
Place beef on a grill rack coated with cooking spray. Drizzle with reserved marinade. Grill 5 minutes on each side or until the meat reaches your desired degree of doneness. Remove from the grill; cover with foil. Let stand for 5 minutes; cut across the grain into thin slices.
Combine the lime juice, 2 tablespoons water, peanut butter, remaining 2 teaspoons sugar, and pepper in a large bowl; stir with a whisk. Add lettuce and the next 4 ingredients; toss to coat. Divide the salad evenly among 4 plates; top evenly with mango. Serve with the beef.