In a medium bowl, whisk together the peanut butter and boiling water. Whisk in the lime juice, cayenne pepper and vinegar.
In large pot bring water to a boil and season with salt. Stir in linguine and cook for 5 minutes. Add carrots to boiling water and cook for 2 minutes. Stir in broccoli and cook for 4 more minutes. Drain linguine and vegetables and transfer to a large bowl. Pour peanut sauce over linguine and vegetables and toss to coat. Toss in peanuts and scallion and garnish with cilantro.