Slice short rib in half and liberally season all sides with kosher salt. Cover with plastic wrap and refrigerate 4hrs to overnight.
Remove short rib 1 hour prior to cooking and let them come to room temperature.
Add cashews to a dry and cold cast-iron skillet. Set the temperature to medium and gently toast the nuts as you gradually preheat the skillet. Once the nuts are warm and fragrant transfer them to a bowl and set aside to cool.
Return skillet to stove and raise heat to high. Pat short ribs very dry with paper towel and rub them with 2-3 tbsp avocado oil. Carefully lay short ribs in the hot pan and cook while continuously turning them every 45-60 seconds until they reach an internal temperature of approximately 120F for a rare to medium-rare centre. *Note: the residual heat in the steak will continue to cook the meat a few more degrees after it has come off the pan.
Let steak rest 5-7 minutes before slicing against the grain.
Meanwhile, to a large mixing bowl, add celery, cucumber, green onion, cilantro, cashews, rice wine vinegar, sesame oil, 1 tbsp avocado oil and a pinch of salt. Toss everything to coat. Taste for seasoning and adjust as required.
Lay celery salad on a serving platter and top with slices of grilled short rib. Garnish with sesame seeds.