Start by heating your pan over high heat. Season the chicken thighs (or breasts) with salt and pepper on both sides.
When the pan is really hot (I usually wait about 2 minutes), add oil, wait 5 seconds, then add chicken with the skin down. Oil may splatter so be careful! I put a lid on to avoid making a mess. Cook until skin is golden brown (about 5-7 minutes).
Flip the chicken over and cook for 2 minutes. Turn the heat off and transfer chicken to a plate covered with paper towel to remove excess oil.
Let cool for 2 minutes (this is to make sure the chicken’s fully cooked as well).
Arrange the chicken on a plate with the skin facing up, cover with chopped scallion and pour a little ponzu over each piece. Serve with Japanese hot mustard.