Whisk together olive oil, lemon juice, garlic and onion powders, rosemary, thyme, salt, pepper, and red pepper flakes.
Put the chicken thighs in a ziplock bag or a non reactive bowl. Pour the marinade over the chicken, coating each piece. Refrigerate for 30 minutes.
Lightly oil the grill grates. Pre heat the gas grill to medium high, or 400°
Place the chicken pieces on the grill, leaving space between them.
Grill over direct heat, 5 minutes each side, (flipping only once), or until a meat thermometer reads 165° when inserted in the thickest part.
Prep time indicated doesn't include marinating time.Trim any excess fat from the boneless thighs before marinating. You can use a sharp knife, but an easy way to do it is with kitchen scissors.Don't marinate overnight, or any longer than 2 hours. If they marinate too long, the acid in the lemon juice will turn the meat mushy. I only marinate this recipe for ½ hour, and the chicken is super flavorful.Use a barbecue brush to clean the grill grates and spray them lightly with cooking spray.While the grill is heating, bring the chicken out of the fridge and using tongs, transfer them to a plate, allowing any excess marinade to drip off.After removing the chicken, discard the chicken thigh marinade. It is not safe to use.Place the boneless thighs on the hot grill, leaving space between them. Close the lid on the grill to maintain the heat.Don't flip until half the cooking time is finished. (Flip only once to avoid sticking).Let the chicken rest for a couple of minutes after removing from the grill. Resting allows the juices to redistribute, so you'll have tender, juicy chicken thighs.Store leftovers in an airtight container in the fridge for up to 3 days.