Grind the fresh coriander with desi ghee and all other marinade ingredients (except yoghurt) into a smooth paste in the food processor. Leave some chopped coriander aside for garnish.
Cut the chicken breast or thighs into 2-inch chunks.
Pour the spice mix into a large bowl and add yoghurt. Mix well. Add the marinade and chicken pieces and stir well. Cover the bowl and refrigerate overnight to marinate.
Thread chicken chunks onto skewers. Preheat the oven to 400 F or the grill to medium-high.
Place the skewers in your oven with a tray underneath to catch drippings or on the grill. Grill for 12 to 15 minutes, until chicken is brown from all sides and tender.
Remove the grilled chicken from skewers and place it on a plate.
Cut the onion into very thin rings and put them in a separate bowl. Squeeze lime juice over them and sprinkle the chaat masala over and mix well till the onions are fully covered. Garnish the grilled chicken tikka with these onion rings and serve with naan.