Open fish like a book. Season cavity of each with salt and pepper, and drizzle with some oil. Stuff with herbs. Close fish, and tie each with kitchen twine at intervals to enclose. Rub both sides of fish with oil.
Toss tomatoes with 1/4 cup oil, salt, and pepper in a bowl.
Working in batches, transfer fish and some tomatoes to a large cast-iron skillet set over a campfire or on a medium-high grill. Grill until fish is browned and crisp, flipping fish and tomatoes halfway through and removing tomatoes as they char, about 14 minutes.