Heat ½ cup distilled white vinegar, 2 Tbsp. sugar, ¼ tsp. black peppercorns, and ¼ tsp. crushed red pepper flakes in a small saucepan, stirring, until sugar is dissolved, about 5 minutes. Remove from heat, add 1 garlic clove, finely grated, and let brine cool.

Toss 8 oz. mixed radishes (such as red and/or watermelon and/or purple daikon), trimmed, thinly sliced, and 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt in a small bowl; let sit until softened and releasing liquid, 10–30 minutes; drain liquid.

Pour brine over radishes. Cover and chill at least 8 hours before using. Do ahead: Radishes can be pickled 1 week ahead. Keep chilled.

Stir ½ cup hoisin sauce, 2 Tbsp. ketchup, 2 Tbsp. light or dark brown sugar, 2 tsp. five-spice powder, 2 tsp. oyster sauce, 2 tsp. soy sauce, 1 tsp. finely grated peeled ginger, 1 tsp. toasted sesame oil, and ¼ cup vegetable oil in a large bowl to combine.

Make shallow cuts along fatty, curved edge of each six ⅓"–¼" bone-in pork rib chops (2–3 lb.) to prevent them from curling as they cook. Add chops to marinade and toss to coat. Cover with a lid or plate and chill at least 2 hours or, preferably, up to 12 hours. Let sit at room temperature 30 minutes before grilling.

Prepare a grill for high heat; oil grate. Remove pork chops from bowl and scrape off excess marinade; discard marinade. Grill, turning often, until deeply browned and an instant-read thermometer inserted near the bone of each registers 140° (internal temperature should climb to 145° as they rest), 8–12 minutes. Transfer to a cutting board and let rest 10 minutes.

Thinly slice meat from bone; transfer to a platter and sprinkle with flaky sea salt. Serve with pickled radishes and red leaf or romaine lettuce leaves.