Season yellowtail fillets with salt and pepper, then lightly coat with flour. Score the scallion pieces with shallow cuts to help them cook evenly and absorb flavor.
Heat oil in a skillet over medium heat. Add the yellowtail and scallions, searing both sides until golden and cooked through.
Pour in the sesame yuzu dressing and simmer briefly to coat the fish and vegetables in the glaze. Serve immediately.