Gently smash each radish with a meat mallet, the side of a knife, or potato smasher until cracked but mostly intact. Place in a bowl, sprinkle with 1 tbsp kosher salt, and toss. Let sit for 30 minutes, then rinse and drain well. Transfer to a large glass jar.
In a small pot, combine rice vinegar, water, coconut sugar, soy sauce, garlic, sriracha, sesame oil, pepper, and the remaining 1 tsp salt. Bring to a simmer, stirring until the sugar dissolves. Remove from heat and let cool slightly.
Pour the brine over the radishes, cover, and refrigerate overnight. If they are not fully submerged, give the jar a shake a few times.
Serve topped with sliced scallions and sesame seeds
