|Written by Jess Gorski|
This recipe uses up more of that cabbage hiding in the back of your crisper and some of those onions we are receiving this week.
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).
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.
Whisk together mayonnaise, crema, 1/2 teaspoon salt, and remaining 3 tablespoons lime juice to make sauce.
Preheat a gas grill with burners on high, covered, 10 minutes, then reduce heat to medium-high.
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.
Wrap tortillas in 2 foil packages and warm on grill, turning once, about 3 minutes total.
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.
Very thinly slice radishes with slicer. Halve, pit, and peel avocados, then cut into 1/2-inch-thick slices. Drain onions.
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.