If you aren't able to grill outdoors, steak can be cooked in a hot lightly oiled well-seasoned skillet or grill- pan over moderately high heat, turning over once, until medium-rare, 12 to 14 minutes total. Dressing can be made 3 hours ahead and kept, covered, at room temperature.
1/4 cup Asian fish sauce
2 tablespoons finely chopped peeled fresh ginger
2 garlic cloves, finely chopped
2 tablespoons soy sauce
2 tablespoons sugar
2 lb flank steak
For salad
1/2 cup fresh lime juice
6 tablespoons water
6 tablespoons sugar
6 tablespoons Asian fish sauce
1 1/2 teaspoons dried hot red-pepper flakes
1/2 cup thinly sliced shallots (2 medium)
8 oz dried vermicelli rice-stick noodles
2 medium Granny Smith apples
7 oz mixed greens salad (16 cups loosely packed)
1 cup fresh mint leaves, torn into pieces if large
1/2 cup salted roasted peanuts (sometimes labeled "cocktail peanuts"), chopped
Whisk together fish sauce, ginger, garlic, soy sauce, and sugar in a small bowl until sugar is dissolved. Pour marinade into a large sealable plastic bag. Pat steak dry and place in bag, then press out excess air and seal bag. Turn bag over 2 or 3 times to coat meat, then place in a shallow dish (in case of leaks) and chill at least 4 hours and up to 8. Bring steak to room temperature 30 minutes before grilling.
Transfer steak to a cutting board and let stand, uncovered, about 15 minutes.
Thinly slice steak across the grain.
Assemble salad while steak rests. Whisk together lime juice, water, sugar, fish sauce, and red-pepper flakes in a bowl until sugar is dissolved, then stir in shallots. Cook noodles in a 5-quart pot of boiling salted water until just tender, 4 to 5 minutes. Drain in a colander, then rinse under cold water and drain well. Transfer to a bowl and toss with 1/2 cup dressing. Working around core of each apple, cut apple in 4 chunks. Slice these approx. 1/4 inch thick. Stack and cut slices lengthwise into matchsticks. Combine apples, greens, and mint in a large bowl. Add 1/2 cup dressing and toss well to coat.
Arrange noodles on a large platter and mound greens on top of noodles. Arrange steak slices on greens and sprinkle with peanuts. Serve at room temperature with remaining dressing on the side.