In glass dish, combine 1 tbsp (15 mL) each of the fish sauce, lime juice and soy sauce and 1 tsp (5 mL) of the sesame oil. Add half each of garlic and ginger. Add steak, turning to coat. Cover and let stand at room temperature for 20 minutes or refrigerate for up to 4 hours.

Meanwhile, in small bowl, stir together remaining fish sauce, lime juice, soy sauce, sesame oil, garlic and ginger. Stir in sugar and red pepper flakes; set dressing aside.

In large bowl, soak noodles in warm water for 20 minutes. Drain and rinse under cold running water. Place in large bowl; toss with dressing.

Cut cucumber in half lengthwise; thinly slice diagonally. Stir into noodles with red pepper and three-quarters of the coriander. Set aside.

Discard marinade, place steak on greased grill over medium-high heat; close lid and grill, turning once, until medium, 10 to 14 minutes, or until desired doneness. Let rest for 10 minutes; slice thinly against the grain. Gently stir into noodle mixture along with the tomatoes.

Line platter with lettuce leaves; mound salad on top. Sprinkle with remaining coriander.