Step 1Prepare the garlicky bread crumbs by grinding the bread crumbs, garlic, parsley, lemon zest and 1 tablespoon of olive oil in a blender or food processor.
Step 2Pat the fish dry with a paper towel. Cut 3 or 4 crosswise slashes on each side of the fish, about 1 1/2 inches apart, cutting through the skin into the meat but not all the way through to the bone.
Step 3Place the fish on a large platter and season inside and out with salt; we used about 1 teaspoon per fish. Whisk together one-third cup olive oil and the lemon juice and pour it over the fish. Turn the fish and drizzle until they are well-coated with olive oil. Sprinkle the bread crumbs over the top and keep turning the fish until they are well-coated with oil-soaked bread crumbs. Press firmly to secure the crumbs. Stuff the body cavities with the herb trimmings.
Step 4Leave the fish at cool room temperature for at least 30 minutes. Alternatively, cover the fish with plastic wrap and refrigerate for at least an hour. As the bread crumbs soften and swell, pat them firmly into place, filling the slashes and crevices and scattering some into the bellies.
Step 5Cut the tomatoes in half if they are small, in quarters if they are large. Peel and seed the cucumbers and cut them crosswise in half-inch pieces. Combine the tomatoes and the cucumbers in a bowl and season with 2 tablespoons of olive oil, the red wine vinegar, fresh basil and salt and pepper. Toss to combine.
Step 6When ready to cook, prepare a medium-hot fire in the grill. You should be able to hold your hand 3 to 4 inches above the surface for 4 to 5 seconds. Make sure the grill is very clean. Using a pair of tongs, rub the grill surface with a paper towel dipped in oil.
Step 7Gently shake any loose bread crumbs from the fish and place the fish on the grill. Cook the fish, without moving them around, until the undersides are well-browned and the flesh begins to flake. This will take 5 or 6 minutes. Don't worry if some of the bread crumbs blacken. If you try to turn the fish and they stick, let them cook another 30 seconds or so to release and try again. Turn and cook on the other side for an additional 5 or 6 minutes.
Step 8Remove fish to a platter; scatter tomato-cucumber salad around the outside. Serve immediately.