Prepare the marinade by adding the tequila, lime juice and zest, salt, pepper, brown sugar, oregano, ancho chile powder, garlic, and cilantro to a medium-sized bowl.
Whisk the ingredients together.
Add the chicken thighs to a baking dish in a single layer and pour over the marinade.
Cover and refrigerate for at least 4 hours and up to overnight. Flip the chicken once in the marinade.
Preheat a grill to 400 F.
Remove the chicken from the marinade, place it on the barbecue, and grill on one side for 5 minutes.
Flip the chicken and grill for 5 more minutes, until it reaches an internal temperature of 165 F.
Serve, garnished with more minced cilantro and lime slices, if desired.