In a dry pan on medium heat, toast the coriander seed and white peppercorns until fragrant. Add to a mortar and pestle with the minced lemongrass and pound into a fine consistency/paste. Add this to a bowl with all of the other marinade ingredients and combine evenly. Add the chicken thighs and toss to coat evenly. Set aside for at least 30 minutes, up to 4 hours.

Heat the grill on high for 15 minutes. Reduce the temperature (if using a gas grill) and spray the grill grate carefully with the avocado oil (spray in short bursts to avoid catching fire).

Grill the chicken on each side until charring develops, but don't let it burn. Move the chicken to the warming rack on the grill, cover with the lid and finish cooking through for another 10 minutes, until internal temp of 175 is reached (thighs are better cooked to a higher temp - trust me).

Remove from heat and let rest for 10 minutes. Serve warm with rice, noodles, salad - anything! Great with Nuoc Cham (sweet fish sauce).