To make the sauce, puree the peppers, lemon juice, and garlic in a food processor. With the machine running, add the oil. Season with the salt. Pour into a bowl and let stand at room temperature until ready to serve, up to 2 hours, or refrigerate for up to one day. (Remove chilled sauce from refrigerator 1 hour before serving.)
Combine the fish and marinade in a zipped plastic bag. Seal the bag and let stand at room temperature for 30 minutes, no longer.
Build a charcoal fire (use about 2 1/2 pounds of briquettes) on one side of an outdoor grill and let it burn until the coals are covered with white ash. In a gas grill, preheat on High, then turn one burner off and adjust the other burner(s) to High.
Lightly oil the cooking grate. Drain the fish well, but do not scrape off the clinging herbs. Place the fish over the coals and cover. Grill, turning occasionally, until browned on all sides, about 6 minutes. In a gas grill, place the fish over the High burner and cover. Grill, turning occasionally, until browned on all sides, about 6 minutes.
Transfer the fish to the cooler side of the grill (or over the off burner). Cook until the fish is opaque when flaked in the center, about 6 more minutes.
Cut each fillet crosswise into thick slices. Transfer the slices to dinner plates. Stir the basil into the sauce. Serve the fish immediately, with the sauce passed on the side.
In a medium glass or nonreactive bowl, whisk together all the ingredients, except the oil. Gradually whisk in the oil. Use immediately or cover with plastic wrap and store in the refrigerator for up to 1 day.
All recipes courtesy of Joe Bonanno, " The Firehouse Grilling Cookbook"