If you don’t like whole fish, you can make this dish with a thick white fish filet, such as halibut. Cut a pocket into the side, and stuff the pocket with the herbs.
Preheat oven to 400 degrees F. With the blunt side of a heavy knife, pound the lemongrass stalks to flatten them slightly. Cut each stalk in half. Stuff 1 stalk, one-sixth of the ginger, and 1 sprig of each herb into the cavity of each trout. Mix the flour, salt, and pepper in a large shallow pan. Coat each trout with the seasoned flour and set aside.
Heat the oil in a large ovenproof saute pan over medium-high heat until nearly smoking. Add the trout and cook until the underside is browned, about 1 minute. Flip the trout and brown the other side.
Transfer the pan to the oven. Bake until the flesh is opaque and flaky, about 4 minutes. Place 1 trout on each plate; garnish with remaining basil, mint, and cilantro sprigs. Serve with Scallion Pancakes.