Active Time

　　45 min

　　Total Time

　　45 min

　　

Ingredients

6 servings

　　1 medium red onion

　　1/2 cup cider vinegar

　　1/4 cup sugar

　　7 tablespoons fresh lime juice, divided

　　1/4 cup chopped cilantro

　　1 tablespoon olive oil

　　1 1/4 pound (1-inch-thick) skinless mahimahi fillet or tuna steak, cut into 12 pieces

　　2/3 cup mayonnaise

　　2/3 cup crema or sour cream

　　12 (6-inch) corn tortillas

　　6 to 8 radishes

　　1 to 2 (6- to 8-ounce) firm-ripe avocados

　　4 cups thinly sliced green cabbage (1/2 small head)

　　Equipment: an adjustable-blade slicer; 12 (6- to 8-inch) wooden skewers, soaked in water 30 minutes

　　Accompaniment: lime wedges

　　

Step 1

Very thinly slice onion crosswise into rings with slicer. Set slicer aside. Heat vinegar, sugar, and 1/2 teaspoon salt in a small heavy nonreactive saucepan until sugar has dissolved. Remove from heat and stir in onion, then let stand until ready to use (about 25 minutes).

　　

Step 2

Meanwhile, stir 1/4 cup lime juice together with cilantro, oil, and 1/2 teaspoon salt. Add fish and toss to coat, then marinate at room temperature 15 minutes.

　　

Step 3

Whisk together mayonnaise, crema, 1/2 teaspoon salt, and remaining 3 tablespoons lime juice to make sauce.

　　

Step 4

Preheat a gas grill with burners on high, covered, 10 minutes, then reduce heat to medium-high.

　　

Step 5

Thread each piece of fish onto a skewer (discard marinade). Wrap exposed part of each skewer in heavy-duty foil to protect it from charring.

　　

Step 6

Wrap tortillas in 2 foil packages and warm on grill, turning once, about 3 minutes total.

　　

Step 7

Oil grill rack, then grill fish, covered, turning once, until opaque and just cooked through (for mahimahi), about 6 minutes total; or until just pink in center (for tuna), about 4 minutes.

　　

Step 8

Very thinly slice radishes with slicer. Halve, pit, and peel avocados, then cut into 1/2-inch-thick slices. Drain onions.

　　

Step 9

Serve fish with tortillas, crema sauce, onions, and remaining toppings.

　　Cooks' Note

　　If you aren't able to grill outdoors, cook fish in a lightly oiled large (2-burner) ridged grill pan. Warm tortillas in foil packages in grill pan 2 to 3 minutes or in a 300°F oven 10 minutes.