Preheat grill to 500F.
Chop parsley, oregano, garlic, shallot and serrano pepper. Add to a medium bowl. Then add salt, pepper, red pepper flakes, olive oil and vinegar. Mix well and set aside.
Add chicken thighs to a bowl. Pour half of the chimichurri sauce on top, reserving the rest to use as a sauce later. Let marinate for 30 minutes.
When the grill is hot, add the chicken. Let cook completely undisturbed for 6-7 minutes before flipping to the other side and allowing to cook for another 6-7 minutes or until fully cooked through (165F internal temp). Note: if your chicken sticks to the grill, that means it's not ready to flip yet!
Serve with the remaining chimichurri and enjoy!
