Preheat oven to 375 degrees. Brush baking sheet with 1 tablespoon olive oil. Place 4 snapper fillets (6 to 8 ounces each), skin side down, on work surface; season with salt and pepper; spread each with 1/2 tablespoon Dijon mustard.
Place 1/2 cup finely chopped assorted fresh herbs on plate; balance strong herbs, such as dill and thyme, with milder ones, such as parsley. Press mustard-coated side of fillets in herbs to coat evenly.
Bake fish on baking sheet, skin side down, until opaque throughout, 12 to 15 minutes. Serve with couscous.