Step 1

For the salsa: Prepare a grill or grill pan for medium heat. When hot, brush generously with vegetable oil.

Step 2

Grill the pineapple rings and scallions (working in batches if using a grill pan), flipping the scallions often, until tender and charred, 3 to 5 minutes total and flipping the pineapple once, until nicely charred, about 5 minutes on each side. Let cool on a cutting board then dice. Toss to combine with the lime juice and salt in a medium bowl. Set aside. (The cilantro and mint will be added just before serving.)

Step 3

For the mahi-mahi: Combine the soy sauce, red pepper flakes, garlic, scallion, ginger, lime juice and reserved pineapple juice in a small saucepan over medium heat. Bring to a simmer and cook until reduced by half, syrupy and thick, about 6 minutes.

Step 4

Pat the mahi-mahi dry with paper towels and generously brush the tops of the fish with the glaze; season with a good pinch each of salt and pepper. Grill glaze-side down, undisturbed, until nicely charred, about 5 minutes. Brush the tops of the fish with glaze and season with another pinch each of salt and pepper. Flip and grill, undisturbed, until the fish is cooked through, 3 to 5 minutes. Brush the tops with more glaze.

Step 5

Divide the fish among plates. Fold the cilantro and mint into the pineapple salsa, then spoon it over the fish. Serve immediately.