In a shallow baking dish, combine the mirin, soy sauce, brown sugar and sesame oil. Add the salmon fillets and let marinate for 3 minutes. Flip and let marinate on the other side.

Heat a large skillet over medium-high heat. Add the salmon fillets and cook for 2 minutes. Flip the salmon over and cook for another 2 – 4 minutes, depending on how done you like your salmon. Remove from pan and pour the marinade into the hot skillet. Add the rice vinegar and cook, stirring until the sauce reduces slightly, about 2 minutes. Pour the sauce over the salmon, garnish with the scallions and sesame seeds. Serve immediately.