In a food processor or blender, combine chipotle, adobo sauce, onion, garlic, cilantro, lime juice, brown sugar, vegetable oil, chicken broth, salt, and pepper.
Pulse or blend sauce several times, scraping down sides as necessary, until sauce is smooth. Season with additional salt and pepper to taste if needed. Reserve 1/4 cup marinade and set aside in refrigerator.
Place chicken thighs in a large bowl and pour remaining marinade over top. Toss chicken to evenly coat in marinade. Cover bowl and marinate chicken in refrigerator 2 hours or up to 12.
When ready to grill, preheat an outdoor grill to medium-high heat or lightly grease and heat a grill pan on stovetop.
Remove chicken from marinade and discard marinade. Grill chicken over medium-high heat, turning occasionally until chicken registers 165F.
Top chicken with a few drizzles of reserved marinade and fresh cilantro and serve warm. Enjoy!