- 2 tablespoons whole-grain mustard
- 1 tablespoon capers, drained
- 1 tablespoon chopped fresh tarragon (optional)
- 4 tablespoons plus 1 teaspoon olive oil
- 4 6-ounce pieces skinless cod, halibut, or striped bass fillet
- kosher salt and black pepper
- 1 large head Bibb lettuce, torn (about 6 cups)
- ½ English cucumber, thinly sliced
- ¼ small red onion, thinly sliced
- 2 tablespoons fresh lemon juice
- In a small bowl, stir together the mustard, capers, tarragon (if using), 2 tablespoons of the oil, and 2 tablespoons water. (If necessary, adjust the consistency with more water until the sauce is spoonable.)
- Heat 1 teaspoon of the remaining oil in a large nonstick skillet over medium-high heat. Season the cod with ½ teaspoon salt and ¼ teaspoon pepper and cook until opaque throughout, 4 to 7 minutes per side.
- Meanwhile, in a large bowl, toss the lettuce, cucumber, and onion with the lemon juice, the remaining 2 tablespoons of oil, and ¼ teaspoon each salt and pepper. Drizzle the cod with the mustard-caper sauce and serve with the salad.