Rub fillets with olive oil and season both sides with salt and pepper. Heat a grill pan over medium-high heat. Grill fish, flipping once, until cooked through, about 4 minutes per side. Flake fish into large pieces, discarding any bones.
Toast corn tortillas over a kitchen burner using tongs or wrap in parchment-lined foil and heat in oven, 5 minutes. Divide fish evenly among tortillas and top with cabbage, radishes, cilantro, and scallions. Season with salt. Serve with yogurt and lime wedges.