In bowl, mix lentils, onion, parsley, 6 tbsp. oil, and vinegar; season. In large nonstick skillet, heat remaining 2 tbsp. oil over medium-high. Season fish; cook, skin-side down, until skin browns, about 3 minutes. Turn; cook until fish is opaque in the center, about 3 minutes more. Serve over lentil salad.
