Mix mayonnaise, onion, pickles, and lemon juice for tartar sauce in a bowl until well combined. Refrigerate until needed.

Combine cabbage, carrots, green onions, and cilantro in a bowl. Mix garlic and ginger with rice vinegar, soy sauce, honey, and sesame oil in a small bowl; pour over slaw and toss to coat. Refrigerate until needed.

Heat 1 1/2 inches oil in a deep pot over medium heat.

While oil is heating, mix flour and baking powder together in a bowl. Slowly add ginger ale and mix to combine. You don’t want the batter to be overly thick; excess batter should be able to coat the fish entirely, but still be able to drip off.

Pat tilapia chunks dry and dredge in the batter until thoroughly coated.

Test the oil by adding a few drops of batter in it; when the batter begins to bubble and float, the oil is ready. Working in batches so you don’t overcrowd the pot, carefully lower some tilapia into the hot oil. Fry until golden brown, 2 to 4 minutes. Transfer to a paper towel-lined plate to drain and sprinkle with salt and pepper. Repeat with remaining tilapia.

To serve, place slaw on warm tortillas. Top with tilapia and tartar sauce.