Preheat your grill or a grill pan over medium-high heat.
Rub the skirt steak with olive oil and season generously with salt and pepper.
In a blender or food processor, combine the avocado, parsley, cilantro, garlic, red chili (if using), red wine vinegar, lime juice, salt, and black pepper. Blend until smooth.
Slowly drizzle in the olive oil while blending until the chimichurri is well combined and creamy.
Grill the skirt steak for about 3-4 minutes per side for medium-rare, or until your desired doneness is reached.
Remove from the grill and let it rest for 5 minutes before slicing against the grain.
Serve the sliced steak topped with the avocado chimichurri.