Grilling whole stuffed fish is not as tricky as it sounds. We tie ours with kitchen twine,which makes them easy to handle.
1/4 small white onion,finely chopped
1/2 cup finely chopped fresh cilantro
1/4 cup fresh lime juice
1 tsp grated peeled ginger
1 tsp sugar
1/2 cup finely chopped fresh mint plus 4 sprigs for stuffing
2 red chiles (such as Fresno or serrano), with seeds,thinly sliced,divided
1/3 cup plus 1 tbsp vegetable oil
Kosher salt
2 whole branzino or small red snapper,cleaned
1 lime, thinly sliced
Prepare grill for medium high heat.Mix onion,cilantro,lime juice,ginger,sugar,chopped mint,half of chiles, and 1/3 cup oil in a medium bowl; season with salt. Set relish aside.
Season inside of fish with salt. Stuff with mint sprigs, lime slices, and remaining chiles; tie with kitchen twine. Drizzle with remaining 1 tbsp oil; season with salt. Grill fish until skin is crisp and flesh is flaky and opaque down to the bone, about 5 minutes per side. ( If asmall knife slides easily through the thickest part of flesh, the fish is done.) Serve with relish.
DO AHEAD:
Fish can be stuffed and tied and relish can be made 6 hours ahead. Cover separately and chill.