Bring a large saucepan of water to a boil. Add noodles, turn off heat and let soak 6 to 8 minutes.
Meanwhile, in a small bowl, whisk vinegar, soy sauce, peanut butter, fish sauce, warm water, sugar and red pepper flakes until smooth. Peel, halve and slice cucumber into half-moons.
Heat grill pan or broiler. Place meat in a resealable plastic bag or a glass dish. Add 3 tbsp of the dressing, turning to coat.
Place remaining dressing in a small saucepan with cornstarch. Bring to a boil; boil 2 minutes. Remove from heat.
Grill or broil meat 6 minutes, turning once, until cooked through.
Drain and rinse noodles and transfer to a large bowl. Add sweet pepper, shredded carrot, cucumber, scallions and sliced cilantro. Drizzle dressing into bowl and toss to combine. Divide among 4 bowls. Slice chicken, pork or beef and divide among bowls. Sprinkle with cilantro leaves and chopped peanuts. Serve each bowl with a lime wedge.
To save even more time, buy precooked chicken from the deli counter, slice and serve over noodle mixture. Swap in a reduced-calorie bottled Asian sesame salad dressing or peanut sauce for the dressing made here.