How to Make It
In a food processor, puree the red chile with the kosher salt until the salt is pink with flecks of chile. Transfer to an airtight container.
Light a grill or heat a nonstick grill pan. Oil the grate or the pan. Brush the fish with grapeseed oil and season with pink chile salt. Grill over moderate heat, turning once, until just cooked through, about 5 minutes.
Meanwhile, in a large bowl, cover the onion with the vinegar and let stand for 5 minutes. Add the radishes, kohlrabi and the 2 tablespoons of grapeseed oil and toss well. Season the salad with pink chile salt and toss again.
Transfer the snapper fillets to plates and serve the radish salad alongside, garnished with radish sprouts.