Rib Eye Aguachile with Ponzu Sauce

Combine soy sauce, orange juice, 1/2 cup cilantro leaves, 5 tablespoons water, rice vinegar, lemongrass, mirin, ginger, and Thai chiles in a blender; process until smooth, about 1 minute. Transfer mixture to a medium saucepan; bring to a simmer over medium. Simmer, undisturbed, until flavors meld, about 10 minutes. Remove from heat; let steep, uncovered, 10 minutes. Pour through a fine wire-mesh strainer into a medium bowl; discard solids. Rinse pan, and wipe dry. Return soy sauce mixture to pan, and return to a simmer over medium. Whisk together cornstarch and remaining 2 tablespoons water in a small bowl to form a slurry. Add cornstarch slurry to simmering soy sauce mixture; simmer, stirring constantly, until mixture is just thick enough to coat the back of a spoon, about 5 minutes. Remove from heat; let ponzu cool completely, about 20 minutes. Refrigerate, covered, until ready to use or up to 3 days.

Place tomatillos on a large plate or baking sheet, and sprinkle evenly with 1/2 teaspoon kosher salt. Set tomatillos aside until ready to use.

Light a charcoal chimney starter filled with briquettes. When briquettes are covered with gray ash, pour them onto bottom grate of grill, and push to one side of grill. Place oak wood chunks over hot coals. Adjust vents as needed to maintain an internal temperature of 250°F to 300°F. Coat top grate with oil; place on grill. Sprinkle steak evenly with pepper and remaining 1/2 teaspoon kosher salt. Place steak on oiled grate over side of grill without coals. Grill, covered, until a thermometer inserted in thickest portion of meat registers 85°F, about 20 minutes. Flip steak; grill, covered, until thermometer registers 100°F, about 10 minutes. Move steak to side of grill with coals. Grill, uncovered, flipping often, until thermometer inserted in thickest portion of meat registers between 115°F and 120°F for rare, about 5 minutes, or to desired degree of doneness. Transfer to a cutting board. Tent with aluminum foil, and let rest 12 to 15 minutes to allow juices to redistribute in steak. Using a sharp knife, cut meat away from bone in 1 piece. Cut meat against the grain into 1/2-inch-thick slices.

Combine onion, cucumbers, tomatillos, and remaining 1/2 cup cilantro leaves in a medium bowl; toss to combine. Spoon ponzu onto a rimmed 12-inch plate; top with steak. Arrange tomatillo mixture on and around steak. Sprinkle with flaky sea salt, and serve.