A crusty, high-quality sourdough will stand up to the seeded salsa verde here and keep the bread from disintegrating. Chef Caroline Glover uses cucumbers from Row 7, a co-op of chefs and plant breeders; you can order the seeds at row7seeds.com. Persian cucumbers, which are more widely available, are a great substitute.
How to Make It
Preheat grill to high (450°F to 500°F). Rub steaks with 1 tablespoon olive oil, and sprinkle with 2 teaspoons kosher salt and 1 teaspoon pepper. Let stand at room temperature 30 minutes.
Meanwhile, place cucumber halves, cut sides down, on oiled grates. Grill, uncovered and without turning, until cut sides are blackened, 10 to 15 minutes. Remove from grill, and set aside to cool completely, about 30 minutes.
Drizzle both sides of bread slices with remaining 1/4 cup olive oil, and sprinkle with 3/4 teaspoon kosher salt and 1/4 teaspoon pepper. Place on grates, and grill, uncovered, turning occasionally, until charred but still chewy, 3 to 4 minutes. Remove from grill, and let cool slightly, about 5 minutes. Tear bread into 1-inch pieces, and toss with 1/2 teaspoon kosher salt and 1/4 teaspoon pepper. Set aside.
Place steaks on oiled grates. Grill, uncovered, until medium-rare, 4 to 5 minutes on each side, or to desired degree of doneness. Transfer steaks to a cutting board, and let rest 10 minutes before thinly slicing against the grain.
Combine cooled cucumber halves, rice vinegar, Dijon, honey, garlic, and 3/4 teaspoon kosher salt in a blender. Process until smooth, about 20 seconds. Add rice bran oil; process until just incorporated, about 8 seconds. Transfer mixture to a large bowl; add bread pieces, and toss to coat. Let stand until slightly softened, about 3 minutes. Add tomatoes, cucumber slices, onion slices, sherry vinegar, remaining 1/2 teaspoon kosher salt, and remaining 1/4 teaspoon pepper; gently fold to combine. Finish with a drizzle of olive oil, and garnish with black pepper, flaky sea salt, and basil leaves. Serve panzanella with steak and salsa verde.