1. Preheat oven to 425°.
2. Combine first 3 ingredients in a bowl. Stir in cabbage and 1/8 teaspoon pepper; cover and chill.
3. Sprinkle both sides of fish evenly with salt and remaining 1/8 teaspoon pepper. Combine potato flakes and Greek seasoning in a shallow dish. Dredge fish in potato flake mixture, pressing firmly to coat.
4. Heat oil in a large ovenproof skillet over medium-high heat. Add fish to pan; cook 2 minutes. Turn fish over; place pan in oven. Bake at 425° for 8 to 9 minutes or until fish flakes easily when tested with a fork.
5. Place about 1/4 cup cabbage mixture on bottom half of each bun; top each with fish and top half of bun. Serve immediately.