For rub, in a food processor bowl or blender container, combine green onions, lemon grass, ginger, and the 6 cloves garlic. Cover and process or blend with a few on-off turns until mixture forms a paste. Use your fingers to rub lemon grass-ginger paste evenly onto both sides of chicken breast halves.
Grill chicken on the rack of an uncovered grill directly over medium coals for 12 to 15 minutes or until chicken is tender and no longer pink, turning once halfway through grilling. Cut chicken into thin, diagonal slices. Set chicken aside.
Meanwhile, cook noodles in a large amount of boiling water for 3 to 4 minutes or until just tender; drain. In a medium bowl combine fish sauce, juice, brown sugar, and the 1 to 2 cloves garlic; stir until brown sugar dissolves. Add hot cooked noodles, carrots, cilantro, and peanuts; toss lightly to coat.
Arrange sliced chicken over hot noodle mixture. Serve immediately. Makes 4 servings.