Combine sesame oil, tamari soy sauce, balsamic vinegar, sriracha, and brown sugar in a bowl, then whisk to combine. Place ribeye in a large glass container, then pour marinade on top. Cover tightly and refrigerate.
When you're ready to begin cooking, take the steak out of the refrigerator and allow it to come to room temperature.
Carefully lift the ribeye steak out of the marinade, allowing excess to drip off. Place gently in the hot skillet.
Using tongs, carefully flip the steak, until a deep crust forms. Cook. We recommend using a meat thermometer to ensure proper doneness. The sauce will bubble and the sugar will start to caramelize.
Once ribeye has reached desired temperature, use tongs to transfer steak to a cutting board. Allow meat to rest.
Use a sharp knife to slice the ribeye into pieces. Garnish with sesame seeds and scallions, then serve immediately.