Chop the red onion into 1 inch chunks and set aside for later. Cut 1 lb chicken thighs into 1-1.5 inch pieces and place the pieces into a large resealable bag or bowl. Set aside.
In a blender, add the herbs, buttermilk, lemon juice, garlic, miso, honey, salt, pepper, cumin seeds, chili flakes, and olive oil. Blend and taste for salt. Reserve ½ cup of the marinade/sauce in a small bowl for serving and set in the fridge.
Pour the rest of the marinade into the bag or bowl of chicken pieces and let marinate for at least 1 hour, up to 24 hours.
Oven-charring: Place the rack in your oven to the second highest level. Preheat your toaster oven or oven to broil on “high.” Line a baking sheet with aluminum foil and drizzle with some olive oil. Assemble the skewers, adding a piece of chicken alternating with a piece of red onion, leaving 2 inches open on each side of the skewer. Place the skewers on the lined tray, one end of the skewer propped up on the edge of the baking tray. Place the skewers in the oven for 7 minutes on broil. After 7 minutes and the onion is visibly charred, remove from the oven and turn the skewers over. Place back in the oven to evenly char the other side for another 7-8 minutes.
Remove from the oven when bits of the chicken are charred. Serve immediately with your reserved green sauce!