Cook the farro according to the package directions. Combine the farro, cabbage, apple, cilantro, vinegar, 2 tablespoons of the oil, ½ teaspoon salt, and ¼ teaspoon black pepper in a large bowl.
Heat the remaining tablespoon of oil in a large nonstick skillet over medium-high heat. Season the fish with the cayenne and ½ teaspoon salt. Cook, in 2 batches, until opaque throughout, 3 to 4 minutes per side.
Serve the fish warm alongside the slaw.
Made the farro slaw and it was delicious, and even better the next day for lunch.