Combine the grapeseed oil, lime juice and coriander in a bowl. Marinate the chicken in that mixture for 10 minutes.
Pre heat a grill or sauté pan to medium high heat. Remove the chicken from the marinade and cook a few minutes on each side until opaque and cooked through.
Roast the tomatillos 4 inches from the broiler until blotchy, blackened and soft. This will take about 5 minutes. Flip them over and roast the other side. The tomatillos will turn from a bright lime green to an olive green. Cool, then transfer them to a blender. Blend the tomatillos with the cilantro, garlic, serrano/jalapeno and lime. Season with salt to taste.
Skewer the chicken when it has cooled to the touch. Dip in the chimichurri tomatillo sauce.