1Toss the pineapple, cilantro, red onion, and lime juice together in a bowl until evenly mixed; set aside.
2Rub the mahi mahi fillets with the sesame oil to lightly coat.
3Sprinkle the sesame seeds evenly over one side of each fillets; gently press the seeds into the fish to assure they stick.
4Heat the vegetable oil in a large non-stick skillet over medium heat.
5Lay the fillets with the seeded side down into the hot oil; cook for 4 minutes, turn, and continue cooking until the flesh turns opaque and flakes easily with a fork, another 3 to 5 minutes. Serve with the pineapple mixture.