In a small bowl, mix together chopped cilantro, olive oil, minced garlic, 1/4 teaspoon of the salt and 1/8 teaspoon of the pepper; set aside.

In medium bowl, mix together brown sugar, mustard, hoisin sauce and vinegar. Reserve 2/3 of this mixture. To remainder, add 1/2 cup lime juice and stir in chicken; cover and refrigerate.

Place sweet potatoes in a heavy saucepan and cover with boiling water. Cook, covered, over medium-high heat until tender, about 15 minutes. Reserve 1/4 cup cooking liquid, then drain potatoes in colander. Return potatoes to reserved cooking water and add butter, chipotle pepper, adobo sauce, remaining 1 1/2 teaspoons lime juice, cumin, lime zest, remaining 1/4 teaspoon salt and remaining 1/8 teaspoon pepper. Mash potatoes.

Preheat the broiler. Thread chicken on 8 bamboo skewers that have been soaked in water for 30 minutes. Broil about 6 inches from heat, basting with reserved mahogany sauce until done, about 8 minutes. To serve, divide potatoes among 4 plates; top each with 2 skewers of chicken and drizzle with cilantro chimichurri sauce. Garnish with cilantro sprigs.