Step 1

Place fish on a cutting board and pat dry thoroughly with paper towels. With a sharp knife, make slashes crosswise on a diagonal along the body every 2" on both sides, cutting all the way down to the bones. Season fish generously inside and out with salt. Coat fish with spice mix, packing on more if needed (it should cover the entire fish, head to tail). Let sit at room temperature 20 minutes.

Step 2

Meanwhile, prepare a grill for medium-high heat. Clean and oil grate.

Step 3

Drizzle both sides of fish with remaining ⅓ cup vegetable oil to coat. Grill fish undisturbed, 10 minutes. Lift up slightly from one edge to see if skin is puffed and lightly charred and easily releases from grate. If not quite ready, leave alone for another minute or so and try again. Once it is ready, gently slide 2 large metal spatulas underneath and turn over.

Step 4

Grill fish until the other side is lightly charred and skin is puffed, 8–12 minutes, depending on the size of the fish. Transfer to a platter.

Step 5

Toss mango, onion, cilantro, lime juice, and a big pinch of salt in a medium bowl. Drizzle with a bit of olive oil and toss again to coat. Scatter mango salad over fish and serve with lime wedges for squeezing over.