In a large mixing bowl, combine the coconut aminos (or soy sauce), pure maple syrup, rice vinegar, toasted sesame oil, minced garlic, grated ginger, gochujang, and black pepper. Whisk together until well combined.
Add the sliced ribeye or NY strip steak to the marinade, ensuring each piece is well coated. Cover the bowl with plastic wrap and let it marinate in the refrigerator for at least 30 minutes, or up to 2 hours for deeper flavor.
Heat the avocado oil in a large skillet or wok over medium-high heat. Once hot, add the marinated beef in a single layer, cooking in batches if necessary to avoid overcrowding the pan. Stir-fry for about 3-5 minutes, or until the beef is cooked through and caramelized on the edges.
Remove the beef from the heat and serve it over a bed of warm cooked white rice. Garnish with chopped green onions and a sprinkle of sesame seeds for that perfect finishing touch.