Combine beef and lemongrass mixture in a large zip-top plastic bag. Seal and marinate in refrigerator 2 to 4 hours.
Remove beef from bag; discard marinade. Place beef on grill rack coated with cooking spray; grill 1 minute on each side or until desired degree of doneness.
Bring a large pot of water to a rolling boil. Add the rice vermicelli and stir gently to loosen them. Cook until the noodles are white and soft but still slightly resilient, about 4 minutes.
Drain and rinse under cold running water.
Gently fluff the noodles and set them aside for at least 30 minutes. The noodles should be dry before serving.
Gently combine all ingredients, top with peanuts and serve with your favorite egg rolls.