Preheat your grill. Real wood charcoal tastes best, but gas works fine. Avoid instant-light briquettes as they make food taste like lighter fluid. Aim for medium heat – if your grill lid has a thermometer built into the lid, it should read about 350 degrees.
Slice the head of lettuce in half lengthwise and rub each half with 1 teaspoon olive oil and 1/4 teaspoon sea salt.
For the bread, butter each side and sprinkle with the Herbes de Provence and 1/4 teaspoon salt.
Place the lettuce and bread on the grill, rotating once during grilling. Lettuce should be slightly charred and just beginning to wilt while bread should be toasted, 4 to 5 minutes. Remove from grill.
Combine tomatoes, cucumber, red onion and basil in a large bowl.
In a separate bowl, whisk together the 3 teaspoons olive oil, champagne vinegar, black pepper, mustard and 1/4 teaspoon sea salt. Pour over the tomatoes mixture and toss until well combined.
To assemble salad, place romaine halves on a platter. Cut toasted bread into small pieces and toss with the tomato mixture. Spoon tomato mixture over salad and serve.