Prepare the sauce first. Place whole tomatillos and pepper in a small pot and cover with water and bring to a boil. Cook until the tomatillos have transformed from their bright green raw state to a dull green, about 10 minutes. Drain water off and transfer to a blender. Let sit for at least 5 minutes and drain any accumulated water. Add onion, garlic, and salt. Process until completely smooth. Set aside.

While the sauce cooks, prepare the beef. Season on both sides with the coriander, cumin, garlic, soy, and monk fruit. Heat a large cast iron pan over medium-medium high. When hot, add a bit of avocado oil and when the oil is hot, add the skirt steak, pressing to ensure good contact with the pan for the best sear. Cook for about 3 minutes per side for medium-rare, or until desired doneness. Let the steak rest for 10 minutes before slicing against the grain for the most tender result.

Spoon salsa verde onto serving plates, top with sliced steak and sprinkle with diced tomato and avocado. Garnish with fresh cilantro, if desired and serve.