In a small bowl whisk together the lemon juice, zest, mustard, tarragon, and chives or scallions, then gradually whisk in the olive oil until well incorporated to make the marinade; season to taste with salt and freshly ground pepper.
Place fish steaks in a Ziplock bag (or use a large shallow non-reactive dish w/ cover), then add the marinade, close the bag securely, and refrigerate for 30 minutes to 2 hours.
Prepare your barbecue or grill pan to medium temperature.
Grill the fish about 3 inches from the coals, or in the grill pan, for 5 to 7 minutes on each side or to desired doneness.
Transfer steaks to a serving platter, garnish with lemon slices and tarragon, and serve immediately.
Goes nicely with a rice salad!
Note: you can also use this recipe with salmon steaks or fillets.
Source: The Taste of Summer by Diane Rossen Worthington, and Moyn at Gail’s Recipe Swap.