Season fish fillet with salt and pepper. In a medium skillet heat 1 tablespoon oil until rippling. Add fish, skinned-side up and sear for 3 minutes. Add lentils, olives, tomatoes and shallots. Using a spoon gently stir vegetables. Turn fish and cook for 2 minutes. Add vinegar and cook 30 seconds. Add stock, bring to a boil and reduce liquids by half. When fish is tender and cooked through, transfer it to a dinner plate. Add remaining olive oil, stirring quickly to work it into sauce. Taste and adjust seasonings. Pour sauce over fish and garnish with parsley.