In a large pot, cook soba noodles according to package directions. Drain, rinse noodles with cold water, and set aside.
Pour into a large bowl the sesame oil, rice vinegar, soy sauce, and lime juice. Mix in lime zest, brown sugar, garlic, and red pepper flakes; stir until sugar dissolves. Toss in carrots, peanuts, and cilantro.
Cut noodles into 3-inch lengths. Stir into dressing mixture. Cover, and refrigerate at least 1 hour.
Toss salad again before serving. If dry, splash with soy sauce and vinegar. Serve cold.