Cook noodles: Bring a medium pot of salted water to a boil. Add noodles to boiling water and cook, stirring frequently, until tender, 5–7 minutes. Drain and rinse noodles under warm water. Using kitchen scissors, cut noodles in half directly in the colander.
Prep ingredients: Trim ends from carrots, then scrub and thinly slice crosswise (no need to peel). Halve pepper, remove stem and seeds, then cut into 1⁄2-inch pieces. Trim ends from celery and thinly slice crosswise. Trim ends from scallions, then cut into 1- inch pieces. Pick 2 tablespoons cilantro leaves and reserve for step 6. Finely chop remaining cilantro leaves and stems.
Make broth: Squeeze 1 tablespoon lime juice, then cut any remaining lime into wedges. In a medium bowl, whisk coconut milk powder with 2⁄3 cup warm water. Stir in lime juice, 1 of the Sriracha packets, 1 teaspoon salt, 1⁄2 teaspoon sugar, and 1⁄4 teaspoon pepper until combined.
Cook vegetables: In the same skillet, heat reserved fried peanut oil over medium-high. Add carrots and cook until barely crisp- tender, about 2 minutes. Add peppers, celery, and scallions to skillet. Season with a pinch each salt and pepper. Cook, stirring frequently, until crisp- tender, about 5 minutes. Add coconut broth and chopped cilantro to the skillet.
Finish & serve: Add noodles. Stir gently to combine and cook until warm, about 1 minute. Remove skillet from heat. Season to taste with salt and pepper. Spoon into bowls, top with fried peanuts and reserved whole cilantro. Drizzle with remaining Sriracha, if desired, and serve with any lime wedges.